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Astrophysics

Thu, 26 Jul 2018

Showing 278 entries from Thu, 19 Jul 2018 to Wed, 25 Jul 2018

Submitted Wed, 25 Jul 2018

[1] arXiv:1807.09750v1 [pdf, vox]

Bright gamma-ray flares powered by magnetic reconnection in QED-strength magnetic fields

K. M. Schoeffler, T. Grismayer, D. Uzdensky, R. A. Fonseca, L. O. Silva
Submitted Wednesday 25 July 2018 @ 17:55:09 GMT

Strong magnetic fields in magnetospheres of neutron stars (especially magnetars) and other astrophysical objects may release their energy in violent, intense episodes of magnetic reconnection. While reconnection has been studied extensively, the extreme field strength near neutron stars introduces new effects: synchrotron cooling and electron-positron pair production. Using massively parallel particle-in-cell simulations that self-consistently incorporate these new quantum-electrodynam​ic effects, we investigate relativistic magnetic reconnection in the strong-field regime. We show that reconnection in this regime can efficiently convert magnetic energy to X-ray and gamma-ray radiation and thus power bright high-energy astrophysical flares. Rapid radiative cooling causes strong plasma and magnetic field compression in compact plasmoids. In the most extreme cases, the field can approach the critical quantum limit, leading to copious pair production.

[2] arXiv:1807.09726v1 [pdf, vox]

Cosmic rays from supernova remnants and superbubbles

Richard E. Lingenfelter
Submitted Wednesday 25 July 2018 @ 17:17:01 GMT
24 pages, 8 figures

Recent high energy gamma-ray observations of both single supernova remnants and superbubbles, together with observations of supernovae, star formation regions, and local cosmic ray composition, now provide an integrated framework tying together the sources, injection, acceleration and propagation of the cosmic rays, so that it is possible to determine their relative contributions to cosmic ray acceleration for all but the very highest energies.

[3] arXiv:1807.09716v1 [pdf, vox]

Evidence of Low-latitude Fluvial and Glacial Activity during the Martian Amazonian Era

Michael F. Zeilnhofer, Colin Orion Chandler, Nadine G. Barlow
Submitted Wednesday 25 July 2018 @ 16:41:18 GMT

The Martian obliquity cycle is predominately influenced by Solar and Jovian tidal forces. The present-day axial tilt of Mars (25 degrees) is predicted to cycle between 0 degrees and 60 degrees (Mischna & Richardson 2005) with excursions up to 80 degrees(Laskar et al. 2004). We focused on Arabia Terra, a region especially well-suited for studying glacial migration due to its location in the northern mid-latitude (20-40 degrees North, 0-30 degrees East) zone, and its heavily cratered terrain. We created glacial and fluvial morphology distribution maps with the ESRI Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS). We determined the ages of our craters in order to establish a time-domain link between the Martian obliquity cycle and glacial migration; we found the average crater age to be roughly 2 billion years old.

[4] arXiv:1807.09714v1 [pdf, vox]

Kinematics and physical properties of the nearby galaxy NGC 4656 and its TDG candidate

N. Muñoz-Elgueta, S. Torres-Flores, P. Amram, J. A. Hernandez-Jimenez, F. Urrutia-Viscarra, C. Mendes de Oliveira, J. A. Gómez-López
Submitted Wednesday 25 July 2018 @ 16:40:20 GMT
23 pages, 18 figures. Accepted for publication in MNRAS

Interacting galaxies provide us with an excellent laboratory for studying a number of physical phenomena associated with these processes. In this paper, we present a spectroscopic and kinematic analysis of the interacting galaxy NGC 4656 and its companion Tidal Dwarf Galaxy (TDG) candidate, NGC 4656UV. Using Fabry-Perot and GMOS multi-slit data, we investigated the possible origin of NGC 4656UV. We found that NGC 4656UV has a low metallicity (12+log(O/H)$\sim$8.​2) and it follows the mass-metallicity relation (MZR) for normal dwarf galaxies. For NGC 4656, we estimated a flat oxygen abundance gradient of $\beta$ = -0.027$\pm$0.029 dex kpc$^{-1}$, which suggests the presence of gas flows induced by gravitational interactions. By analysing radial velocity profiles and by fitting a kinematic model of the observed velocity field, we confirm the literature result that NGC 4656 consists of one single body instead of two objects. We estimated a dynamical mass of $6.8^{1.8}_{-0.6}\ti​mes10^{9}$ M$_{\odot}$ and R of 12.1 kpc from the kinematic model of NGC 4656. Although the observed velocity field is dominated by rotation at large scales (V$_{max}$/$\sigma\g​trsim$2.8), important non-rotational motions are present at small scales. Based on these new results, and on previously published information, we propose that NGC 4656 and 4656UV are a pair of interacting galaxies. NGC 4656UV is a companion of NGC 4656 and it does not have a tidal origin. The interaction between the two could have triggered the star formation in NGC 4656UV and increased the star formation in the northeast side of NGC 4656.

[5] arXiv:1807.09690v1 [pdf, vox]

LCO observations of a super-critical distorted pulsation in the roAp star J0855 (TYC 2488-1241-1)

Daniel L. Holdsworth, Hideyuki Saio, Ramotholo R. Sefako, Dominic M. Bowman
Submitted Wednesday 25 July 2018 @ 16:10:49 GMT
7 Pages, 6 Figures, 2 Tables. Accepted for publication in MNRAS

We report the results of a 60-hr photometric campaign of a rapidly oscillating Ap star, J0855 (TYC 2488-1241-1). We have utilised the multi-site Las Cumbres Observatory's (LCO) 0.4-m telescopes to obtain short cadence B-band observations of an roAp star previously lacking detailed study. Our observations confirm the rotation period presented in the discovery paper of this star ($P_{\rm rot}=3.0918$ d), and reveal the star to be pulsating in a distorted mode. The B data show this star to be among the highest amplitude roAp stars, with a peak-to-peak amplitude of 24 mmag. Modelling of the pulsation frequency at 197.2714 d$^{-1}$ (2283 $\mu$Hz; P=7.30 min) shows that this star belongs to the subgroup of super-critical pulsators, where the observed frequencies are above the theoretical acoustic cutoff frequency. From the modelling, we deduce that the star's rotation axis is inclination angle of about $30^\circ$ to the line-of-sight, with an angle of obliquity of the magnetic axis to the rotation axis of either $40^\circ$ or $24^\circ$ depending on whether the pulsation mode is dipole or quadrupole, respectively.

[6] arXiv:1807.09649v1 [pdf, vox]

Searching for the weakest detectable magnetic fields in white dwarfs. Highly-sensitive measurements from first VLT and WHT surveys

Stefano Bagnulo, John D. Landstreet
Submitted Wednesday 25 July 2018 @ 14:57:51 GMT
Accepted by A&A

Our knowledge of the magnetism in white dwarfs is based on an observational dataset that is biased in favour of stars with very strong magnetic fields. Most of the field measurements available in the literature have a relatively low sensitivity, while current instruments allow us to detect magnetic fields of white dwarfs with sub-kG precision. With the aim of obtaining a more complete view of the incidence of magnetic fields in degenerate stars, we have started a long-term campaign of high-precision spectropolarimetric observations of white dwarfs. Here we report the results obtained so far with the low-resolution FORS2 instrument of the ESO VLT and the medium-resolution ISIS instrument of the WHT. We have considered a sample of 48 stars, of which five are known magnetic or suspected magnetic stars, and obtained new longitudinal magnetic field measurements with a mean uncertainty of about 0.6 kG. Overall, in the course of our survey (the results of which have been partially published in papers devoted to individual stars) we have discovered one new weak-field magnetic white dwarf, confirmed the magnetic nature of another, found that a suspected magnetic star is not magnetic, and suggested two new candidate magnetic white dwarfs. Even combined with data previously obtained in the literature, our sample is not sufficient yet to reach any final conclusions about the actual incidence of very weak magnetic fields in white dwarfs, but we have set the basis to achieve a homogeneous survey of an unbiased sample of white dwarfs. As a by-product, our survey has also enabled us to carry out a detailed characterisation of the ISIS and the FORS2 instruments for the detection of extremely weak magnetic fields in white dwarfs, and in particular to relate the S/N to measurement uncertainty for white dwarfs of different spectral types. This study will help the optimisation of future observations.

[7] arXiv:1807.09645v1 [pdf, vox]

Ultra-High-Energy Cosmic Rays

Luis A. Anchordoqui
Submitted Wednesday 25 July 2018 @ 14:55:34 GMT
Invited review for Physics Reports. This article will build upon the content of arXiv:hep-ph/0206072​, arXiv:astro-ph/04023​71, arXiv:hep-ph/0407020​, arXiv:1104.0509, arXiv:1307.5312, arXiv:1505.02153, arXiv:1709.07321, arXiv:1801.06160, and arXiv:1801.07170

In this report we review the important progress made in recent years towards understanding the experimental data on ultra-high-energy ($E \gtrsim 10^9$ GeV) cosmic rays. We begin with a general survey of the available data, including a description of the energy spectrum, the nuclear composition, and the distribution of arrival directions. At this point we also give a synopsis of experimental techniques. After that, we introduce the fundamentals of cosmic ray acceleration and energy loss during propagation, with a view of discussing the conjectured nearby sources. Next, we survey the state of the art regarding the high- and ultra-high-energy cosmic neutrinos which should be produced in association with the observed cosmic rays. These neutrinos can constitute key messengers identifying currently unknown cosmic accelerators, possibly in the distant universe, because their propagation is not influenced by background photon or magnetic fields. Subsequently, we summarize the phenomenology of cosmic ray air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra-high energies and the main electromagnetic processes that govern the longitudinal shower evolution. Armed with these two principal shower ingredients and motivation from the underlying physics, we describe the different methods proposed to distinguish the primary particle species. In the end, we explore how ultra-high-energy cosmic rays can be used as probes of beyond standard model physics models.

[8] arXiv:1807.09635v1 [pdf, vox]

Chemistry During the Gas-rich Stage of Planet Formation

Edwin A. Bergin, L. Ilsedore Cleeves
Submitted Wednesday 25 July 2018 @ 14:38:06 GMT
Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018); 29 pages, 12 figures

In this chapter we outline some of the basic understanding of the chemistry that accompanies planet formation. We discuss the basic physical environment which dictates the dominant chemical kinetic pathways for molecule formation. We focus on three zones from both observational and theoretical perspectives: (1) the planet forming midplane and ice/vapor transition zones (snow-lines), (2) the warm disk surface that is shielded from radiation, which can be readily accessed by todays observational facilities, and (3) the surface photodissociation layers where stellar radiation dominates. We end with a discussion of how chemistry influences planet formation along with how to probe the link between formation and ultimate atmospheric composition for gas giants and terrestrial worlds.

[9] arXiv:1807.09631v1 [pdf, vox]

The determination of protoplanetary disk masses

Edwin A. Bergin, Jonathan P. Williams
Submitted Wednesday 25 July 2018 @ 14:29:03 GMT
38 pages, 9 figures; proceedings from conference on Formation, Evolution, and Dynamics of Young Solar Systems. 2017, ASSL, 445, 1

In this article we review the methods used to determine the gas and dust masses of protoplanetary disks, with an emphasis on the lesser characterized total gas mass. Our review encompasses all the indirect tracers and the methodology that is be used to isolate the hidden H2 via dust, CO, and HD emission. We discuss the overall calibration of gaseous tracers which is based on decades of study of the dense phases of the interstellar medium. At present, disk gas masses determined via CO and HD are (in a few instances) different by orders of magnitude, hinting at either significant evolution in total disk mass or in the CO abundance . Either of these would represent a fundamental physical or chemical process that appears to dominate the system on ~million year timescales. Efforts to reconcile these differences using existing and future facilities are discussed.

[10] arXiv:1807.09622v1 [pdf, vox]

Spatially resolved broad-band synchrotron emission from the non-thermal limbs of SN1006

Jiang-Tao Li, Jean Ballet, Marco Miceli, Ping Zhou, Jacco Vink, Yang Chen, Fabio Acero, Anne Decourchelle, Joel N. Bregman
Submitted Wednesday 25 July 2018 @ 14:14:00 GMT
21 pages, 14 figures, 7 tables, ApJ in press

We present ~400ks NuSTAR observations of the northeast (NE) and southwest (SW) non-thermal limbs of the Galactic SNR SN1006. We discovered three sources with X-ray emission detected at >50keV. Two of them are identified as background AGN. We extract the NuSTAR spectra from a few regions along the non-thermal limbs and jointly analyze them with the XMM-Newton spectra and the radio data. The broad-band radio/X-ray spectra can be well described with a synchrotron emission model from a single population of CR electrons with a power law energy distribution and an exponential cutoff. The power law index of the electron particle distribution function (PDF) is ~1.88-1.95 for both the NE and SW limbs, and we do not find significant evidence for a variation of this index at different energy (curvature). There are significant spatial variations of the synchrotron emission parameters. The highest energy electrons are accelerated in regions with the lowest expansion velocity, which is opposite to what has been found in the Tycho's SNR. In addition to a gradual steepening of synchrotron emission from the center of the non-thermal limbs to larger azimuthal angles, we also find that both the emission spectrum and the PDF are significantly flatter in three regions in the SW limb where the shock encounters higher density ambient medium. The NE limb also shows significantly higher cutoff energy in the PDF than the SW limb. By comparing with the roughly symmetric TeV emission and largely asymmetric GeV emission from the two non-thermal limbs, we conclude that the asymmetry in the ambient medium and magnetic fields may have largely modified the acceleration and emission of CR leptons.

[11] arXiv:1807.09608v1 [pdf, vox]

Planets around evolved intermediate-mass stars in open clusters II. Are there really planets around IC4651No9122, NGC2423No3 and NGC4349No127?

E. Delgado Mena, C. Lovis, N. C. Santos, J. Gomes da Silva, A. Mortier, M. Tsantaki, S. G. Sousa, P. Figueira, M. S. Cunha, T. L. Campante, V. Adibekyan, J. P. Faria, M. Montalto
Submitted Wednesday 25 July 2018 @ 13:55:02 GMT
15 pages, 18 figures, accepted by A&A

(shorter version)The aim of this work is to search for planets around intermediate-mass stars in open clusters by using RV data obtained with HARPS from an extensive survey with more than 15 years of observations for a sample of 142 giant stars in 17 open clusters. We present the discovery of a periodic RV signal compatible with the presence of a planet candidate in the 1.15 Gyr open cluster IC4651 orbiting the 2.06 M$_\odot$ star No. 9122. If confirmed, the planet candidate would have a minimum mass of 7.2 M$_{J}$ and a period of 747 days. However, we also find that the FWHM of the CCF varies with a period close to the RV, casting doubts on the planetary nature of the signal. We also provide refined parameters for the previously discovered planet around NGC2423 No. 3 but show evidence that the BIS of the CCF is correlated with the RV during some of the observing periods. This fact advises us that this might not be a real planet and that the RV variations could be caused by stellar activity and/or pulsations. Finally, we show that the previously reported signal by a brown dwarf around NGC4349 No. 127 is presumably produced by stellar activity modulation. The long-term monitoring of several red giants in open clusters has allowed us to find periodic RV variations in several stars. However, we also show that the follow-up of this kind of stars should last more than one orbital period to detect long-term signals of stellar origin. This work warns that although it is possible to detect planets around red giants, large-amplitude, long-period RV modulations do exist in such stars that can mimic the presence of an orbiting planetary body. Therefore, we need to better understand how such RV modulations behave as stars evolve along the RGB and perform a detailed study of all the possible stellar-induced signals (e.g. spots, pulsations, granulation) to comprehend the origin of RV variations.

[12] arXiv:1807.09579v1 [pdf, vox]

The Utility of Lyman-alpha Emission Lines as a Probe of Interactions between High Redshift Galaxies and their Environments

Henry J. T. Childs, Elizabeth R. Stanway
Submitted Wednesday 25 July 2018 @ 13:30:39 GMT
16 pages. Accepted for publication in MNRAS

The Lyman-alpha emission line is the strongest feature in the spectrum of most high redshift galaxies, and is typically observed as being highly asymmetric due to galactic outflows. Quantifying this asymmetry is challenging. Here, we explore how measurements of one parameterisation, Lyman-alpha skewness, are affected by instrumental resolution and detection signal-to-noise and thus whether this can be extended throughout the archive. We model these effects through simulated lines and apply our derived corrections to existing archival data sets (including sources observed with FORS2 and DEIMOS) to reconstruct the intrinsic line emission parameters. We find a large uncertainty in parameter reconstruction at low resolutions (R<3000) and high skew values, as well as substantial random errors resulting from the masking of sky lines. We suggest that interpretations of spectral line asymmetry should be made with caution, while a simpler parametrization, like B/R (blue-red flux asymmetry), is likely to yield more robust results. We see a possible weak trend in velocity width with mass, although there is no evidence in the data for a reliable correlation of skew with galaxy mass, star formation rate or age at z=4-5. Using our results, we investigate the possibilities of recovering emission line asymmetry with current and future instruments.

[13] arXiv:1807.09572v1 [pdf, vox]

A new pulse shape description for $α$ particle pulses in a highly-sensitive sub-Kelvin bolometer

S. L. Stever, F. Couchot, N. Coron, R. M. J. Janssen, B. Maffei
Submitted Wednesday 25 July 2018 @ 13:18:06 GMT
Presented at SPIE Astronomical Telescopes and Instrumentation 2018 (Austin, TX), published in Proc. SPIE 10698, Optical Infrared and Millimetre Wave, 1069863 on 12 July 2018

The next generation of cosmology space missions will be sensitive to parasitic signals arising from cosmic rays. Using a composite bolometer, we have investigated pulses produced by $\alpha$ particles in order to understand the movement of energy produced by ionising radiation. Using a series of measurements at 100 mK, we have compared the typical fitting algorithm (a mathematical model) with a second method of pulse interpretation by convolving the detector's thermal response function with a starting profile of thermalised athermal phonons, taking into account the effects of heat propagation. Using this new fitting method, we have eliminated the need for a non-physical quadratic nonlinearity factor produced using more common methods, and we find a pulse form in good agreement with known aspects of thermal physics. This work is carried forward in the effort to produce a physical model for energy deposition in this detector. The modelling is motivated by the reproduction of statistical features in the experimental dataset, and the new interpretation of $\alpha$ pulse shapes represents an improvement in the current understanding of the energy propagation mechanisms in this detector.

[14] arXiv:1807.09541v1 [pdf, vox]

Influence of Energy-Dependent Particle Diffusion on the X-ray spectral curvature of MKN 421

Pranjupriya Goswami, Sunder Sahayanathan, Atreyee Sinha, Ranjeev Misra, Rupjyoti Gogoi
Submitted Wednesday 25 July 2018 @ 12:10:05 GMT
Accepted for Publication in MNRAS, 9 pages, 4 figures

The X-ray spectral curvature of blazars is traditionally explained by an empirical log-parabola function characterized by three parameters, namely the flux, curvature and spectral index at a given energy. Since their exact relationship with the underlying physical quantities is unclear, interpreting the physical scenario of the source through these parameters is difficult. To attain an insight on the X-ray spectral shape, we perform a detailed study of the X-ray spectra of the blazar MKN 421, using an analytical model where the electron diffusion from the particle acceleration site is energy-dependent. The resultant synchrotron spectrum is again determined by three parameters, namely, the energy index of the escape time scale, the quantity connecting the electron energy to the observed photon energy and the normalization. The X-ray observations of MKN 421, during July 2012 - April 2013 by NuSTAR and Swift-XRT are investigated using this model and we find a significant correlation between model parameters and the observational quantities. Additionally, a strong anti-correlation is found between the fit parameters defining the spectral shape, which was not evident from earlier studies using empirical models. This indicates the flux variations in MKN 421 and possibly other blazars, may arise from a definite physical process that needs to be further investigated.

[15] arXiv:1807.09540v1 [pdf, vox]

Beyond the traditional Line-of-Sight approach of cosmological angular statistics

Nils Schöneberg, Marko Simonović, Julien Lesgourgues, Matias Zaldarriaga
Submitted Wednesday 25 July 2018 @ 11:56:18 GMT
40 pages, 6 figures

We present a new efficient method to compute the angular power spectra of large-scale structure observables that circumvents the numerical integration over Bessel functions, expanding on a recently proposed algorithm based on FFTlog. This new approach has better convergence properties. The method is explicitly implemented in the CLASS code for the case of number count $C_\ell$'s (including redshift-space distortions, weak lensing, and all other relativistic corrections) and cosmic shear $C_\ell$'s. In both cases our approach speeds up the calculation of the exact $C_\ell$'s (without the Limber approximation) by a factor of order 400 at a fixed precision target of 0.1%.

[16] arXiv:1807.09539v1 [pdf, vox]

Supersize me! Jets from massive young stellar objects

Alessio Caratti o Garatti
Submitted Wednesday 25 July 2018 @ 11:55:36 GMT
Published in the "Perspective" section of the Star Formation Newsletter #307 (edited by Bo Reipurth); http://www.ifa.hawai​i.edu/~reipurth/news​letter.htm

This short review examines the most recent observational results obtained for jets driven by high-mass young stellar objects (HMYSOs). Reviewed data range from near-infrared to radio wavelengths, with particular emphasis on the IR regime, and are presented along with perspectives for future observations achievable with newly available or forthcoming facilities.

[17] arXiv:1807.09533v1 [pdf, vox]

Coronal EUV, QFP, and kink waves simultaneously launched during the course of jet-loop interaction

Yuandeng Shen, Zehao Tang, Hongbo Li, Yu Liu
Submitted Wednesday 25 July 2018 @ 11:26:39 GMT
Online published in MNRAS Letters, see https://academic.oup​.com/mnrasl/advance-​article-abstract/doi​/10.1093/mnrasl/sly1​27/5053069?redirecte​dFrom=fulltext

We present the observations of an extreme ultraviolet (EUV) wave, a quasi-periodic fast-propagating (QFP) magnetosonic wave, and a kink wave that were simultaneously associated with the impingement of a coronal jet upon a group of coronal loops. After the interaction, the coronal loop showed obvious kink oscillation that had a period of about 428 seconds. In the meantime, a large-scale EUV wave and a QFP wave are observed on the west of the interaction position. It is interesting that the QFP wave showed refraction effect during its passing through two strong magnetic regions. The angular extent, speed, and lifetime of the EUV (QFP) wave were about 140 (40) degree, 423 (322) km/s, and 6 (26) minutes, respectively. It is measured that the period of the QFP wave was about 390 +/- 100 second. Based on the observational analysis results, we propose that the kink wave was probably excited by the interaction of the jet; the EUV was probably launched by the sudden expansion of the loop system due to the impingement of the coronal jet; and the QFP wave was possibly formed through the dispersive evolution of the disturbance caused by the jet-loop interaction.

[18] arXiv:1807.09509v1 [pdf, vox]

VHE observations of binary systems performed with the MAGIC telescopes

Alicia López-Oramas, Oscar Blanch, Emma de Oña Wilhelmi, Alba Fernández-Barral, Daniela Hadasch, Elena Moretti, Pere Munar-Adrover, Josep Maria Paredes, Marc Ribó, Diego F. Torres, Pol Bordas, François Brun, Jorge Casares, Roberta Zanin
Submitted Wednesday 25 July 2018 @ 10:03:53 GMT
Proceedings of High-Energy Phenomena in Relativistic Outflows (HEPRO) VI conference

The improvement on the Imaging Air Cherenkov Technique (IACT) led to the discovery of a new type of sources that can emit at very high energies: the gamma-ray binaries. Only six systems are part of this exclusive class. We summarize the latest results from the observations performed with the MAGIC telescopes on different systems as the gamma-ray binary LS I +61$^{\circ}$ 303 and the microquasars SS433, V404 Cygni and Cygnus X-1, which are considered potential VHE gamma-ray emitters. The binary system LS I +61$^{\circ}$ 303 has been observed by MAGIC in a long-term monitoring campaign. We show the newest results of our search for super-orbital variability also in context of contemporaneous optical observations. Besides, we will present the results of the only super-critical accretor known in our galaxy: SS 433. We will introduce the VHE results achieved with MAGIC after 100 hours of observations on the microquasar Cygnus X-1 and report on the microquasar V404 Cyg, which has been observed with MAGIC after it went through a series of exceptional X-ray outbursts in June 2015.

[19] arXiv:1807.09507v1 [pdf, vox]

Nuclear $γ$-ray emission from very hot accretion flows

Ervin Kafexhiu, Felix Aharonian, Maxim Barkov
Submitted Wednesday 25 July 2018 @ 09:53:07 GMT
7 pages, 7 figures

The ion temperature in optically thin accretion plasmas, e.g., in the Advection Dominated Accretion Flows (ADAF), can reach $kT_{\rm i}>1$~MeV, and thus trigger nuclear reactions. Using a large nuclear reaction network, we study the radial evolution of the chemical composition of the accretion flow towards the black hole and compute the emissivity in nuclear $\gamma$-ray lines. In the ADAF accretion regime, the CNO and heavier nuclei are destroyed before reaching the last stable orbit. The luminosity in $\gamma$-ray lines can be as high as $5 \times 10^{-4}$ of the accretion luminosity. The efficiency of transformation of the kinetic energy of the outflow into high energy ($\geq 100$~MeV) $\gamma$-rays through the production and decay of $\pi^0$-mesons, can be higher, up to $10^{-2}$ of the accretion luminosity. Neutrons that are produced in nuclear reactions can evaporate from the disk with a rate as large as 15~\% of the accretion rate.

[20] arXiv:1807.09504v1 [pdf, vox]

A more comprehensive habitable zone for finding life on other planets

Ramses M. Ramirez
Submitted Wednesday 25 July 2018 @ 09:48:37 GMT
Accepted in Geosciences. Invited review for publication in "Planetary Evolution and Search for Life on Habitable Planets" Special Issue (58 pages, 15 Figures, 1 Table)

The habitable zone (HZ) is the circular region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. Space missions employ the HZ to select promising targets for follow-up habitability assessment. The classical HZ definition assumes that the most important greenhouse gases for habitable planets orbiting main-sequence stars are CO2 and H2O. Although the classical HZ is an effective navigational tool, recent HZ formulations demonstrate that it cannot thoroughly capture the diversity of habitable exoplanets. Here, I review the planetary and stellar processes considered in both classical and newer HZ formulations. Supplementing the classical HZ with additional considerations from these newer formulations improves our capability to filter out worlds that are unlikely to host life. Such improved HZ tools will be necessary for current and upcoming missions aiming to detect and characterize potentially habitable exoplanets.

[21] arXiv:1807.07459v2 [pdf, vox]

High-velocity hot CO emission close to Sgr A*: Herschel/HIFI submillimeter spectral survey toward Sgr A*

Javier R. Goicoechea, M. G. Santa-Maria, D. Teyssier, J. Cernicharo, M. Gerin, J. Pety
Submitted Wednesday 25 July 2018 @ 09:37:36 GMT
Accepted for publication in A&A Letters ( this v2 includes corrections by language editor)

The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480 to 1250 GHz}) and [CII]158um line observations carried out with Herschel/HIFI toward Sgr A*; these results are complemented by a ~2'x2' CO (J=3-2) map taken with the IRAM 30 m telescope at ~7'' resolution. We report the presence of high positive-velocity emission (up to about +300 km/s) detected in the wings of CO J=5-4 to 10-9 lines. This wing component is also seen in H2O (1_{1,0}-1_{0,1}) a tracer of hot molecular gas; in [CII]158um, an unambiguous tracer of UV radiation; but not in [CI]492,806 GHz. This first measurement of the high-velocity CO rotational ladder toward Sgr A* adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (< 1 pc). Observed by ALMA, this velocity range appears as a collection of CO (J=3-2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer T_k~400 K to 2000 K for n_H~(0.2-1.0)x10^5 cm^-3. These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10-60 M_Sun component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates.

[22] arXiv:1807.09494v1 [pdf, vox]

IR Spectral Fingerprint of Carbon Monoxide in Interstellar Water Ice Models

Lorenzo Zamirri, Silvia Casassa, Albert Rimola, Mireia Segado-Centellas, Cecilia Ceccarelli, Piero Ugliengo
Submitted Wednesday 25 July 2018 @ 09:09:22 GMT
MNRAS, accepted

Carbon monoxide (CO) is the second most abundant molecule in the gas-phase of the interstellar medium. In dense molecular clouds, it is also present in the solid-phase as a constituent of the mixed water-dominated ices covering dust grains. Its presence in the solid-phase is inferred from its infrared (IR) signals. In experimental observations of solid CO/water mixed samples, its IR frequency splits into two components, giving rise to a blue- and a redshifted band. However, in astronomical observations, the former has never been observed. Several attempts have been carried out to explain this peculiar behaviour, but the question still remains open. In this work, we resorted to pure quantum mechanical simulations in order to shed some light on this problem. We adopted different periodic models simulating the CO/H$_2$O ice system, such as single and multiple CO adsorption on water ice surfaces, CO entrapped into water cages and proper CO:H$_2$O mixed ices. We also simulated pure solid CO. The detailed analysis of our data revealed how the quadrupolar character of CO and the dispersive forces with water ice determine the energetic of the CO/H$_2$O ice interaction, as well as the CO spectroscopic behaviour. Our data suggest that the blueshifted peak can be assigned to CO interacting {\it via} the C atom with dangling H atoms of the water ice, while the redshifted one can actually be the result of CO involved in different reciprocal interactions with the water matrix. We also provide a possible explanation for the lack of the blueshifted peak in astronomical spectra. Our aim is not to provide a full account of the various interstellar ices, but rather to elucidate the sensitivity of the CO spectral features to different water ice environments.

[23] arXiv:1807.09489v1 [pdf, vox]

Does slow and steady win the race? Investigating feedback processes in giant molecular clouds

L. Garratt-Smithson, G. A. Wynn, C. Power, C. J. Nixon
Submitted Wednesday 25 July 2018 @ 08:58:42 GMT
35 pages, 46 figures, accepted for publication in MNRAS

We investigate the effects of gradual heating on the evolution of turbulent molecular clouds of mass $2\times 10^6$ M$_\odot$ and virial parameters ranging between $0.7-1.2$. This gradual heating represents the energy output from processes such as winds from massive stars or feedback from High Mass X-ray binaries (HMXBs), contrasting the impulsive energy injection from supernovae (SNe). For stars with a mass high enough that their lifetime is shorter than the life of the cloud, we include a SN feedback prescription. Including both effects, we investigate the interplay between slow and fast forms of feedback and their effectiveness at triggering/suppressi​ng star formation. We find that SN feedback can carve low density chimneys in the gas, offering a path of least resistance for the energy to escape. Once this occurs the more stable, but less energetic, gradual feedback is able to keep the chimneys open. By funneling the hot destructive gas away from the centre of the cloud, chimneys can have a positive effect on both the efficiency and duration of star formation. Moreover, the critical factor is the number of high mass stars and SNe (and any subsequent HMXBs) active within the free-fall time of each cloud. This can vary from cloud to cloud due to the stochasticity of SN delay times and in HMXB formation. However, the defining factor in our simulations is the efficiency of the cooling, which can alter the Jeans mass required for sink particle formation, along with the number of massive stars in the cloud.

[24] arXiv:1807.05784v2 [pdf, vox]

Modelling mid-infrared molecular emission lines from T Tauri stars

P. Woitke, M. Min, W. -F. Thi, C. Roberts, A. Carmona, I. Kamp, F. Menard, C. Pinte
Submitted Wednesday 25 July 2018 @ 08:35:05 GMT
accepted by A&A, 13 figures, 4 tables

We introduce a new modelling framework called FLiTs to simulate infrared line emission spectra from protoplanetary discs. This paper focuses on the mid-IR spectral region between 9.7 um to 40 um for T Tauri stars. The generated spectra contain several tens of thousands of molecular emission lines of H2O, OH, CO, CO2, HCN, C2H2, H2 and a few other molecules, as well as the forbidden atomic emission lines of SI, SII, SIII, SiII, FeII, NeII, NeIII, ArII and ArIII. In contrast to previously published works, we do not treat the abundances of the molecules nor the temperature in the disc as free parameters, but use the complex results of detailed 2D ProDiMo disc models concerning gas and dust temperature structure, and molecular concentrations. FLiTs computes the line emission spectra by ray tracing in an efficient, fast and reliable way. The results are broadly consistent with R=600 Spitzer/IRS observational data of T Tauri stars concerning line strengths, colour, and line ratios. In order to achieve that agreement, however, we need to assume either a high gas/dust mass ratio of order 1000, or the presence of illuminated disc walls at distances of a few au. The molecules in these walls cannot be photo-dissociated easily by UV because of the large densities in the walls which favour their re-formation. Most observable molecular emission lines are found to be optically thick, rendering a standard analysis with column densities difficult. We find that the difference between gas and dust temperatures in the disc surface is important for the line formation. We briefly discuss the effects of C/O ratio and choice of chemical rate network on these results. Our analysis offers new ways to infer the chemical and temperature structure of T Tauri discs from future JWST/MIRI observations, and to possibly detect secondary illuminated disc walls based on their specific mid-IR molecular signature.

[25] arXiv:1807.09471v1 [pdf, vox]

Parameterisation of lateral density and arrival time distributions of Cherenkov photons in EASs as functions of independent shower parameters for different primaries

P. Hazarika, G. S. Das, U. D. Goswami
Submitted Wednesday 25 July 2018 @ 08:09:55 GMT
15 pages and 9 figures

The simulation of Cherenkov photon's lateral density and arrival time distributions in Extensive Air Showers (EASs) was performed with the CORSIKA code in the energy range: 100 GeV to 100 TeV. On the basis of this simulation we obtained a set of approximating functions for the primary $\gamma$-ray photons, protons and iron nuclei incident at zenith angles from 0$^\circ$ to 40$^\circ$ over different altitudes of observation. Such a parameterisation is important for the primary particle identification, for the reconstruction of the shower observables and hence for a more efficient disentanglement of the $\gamma$-ray showers from the hadronic showers. From our parameterisation analysis, we have found that even though the geometry of the lateral density ($\rho_{ch}$) and the arrival time ($t_{ch}$) distributions is different for different primaries at a particular energy ($E$), at a particular incident angle ($\theta$) and at a particular altitude of observation ($H$) up to a given distance from the showe core ($R$), the distributions follow the same mathematical functions $\rho(E,R,\theta,H) = a E^{b}\exp[-\{c R + (\theta /d)^{2}-f H\}]$ and $t(E,R,\theta,H) = l E^{-m}\exp(n/R^{p})(​{\theta}^q+s)(u {H}^2+v)$ respectively but with different values of function parameters.

[26] arXiv:1807.09470v1 [pdf, vox]

Studies on cosmic ray nuclei with Voyager, ACE and AMS-02: I. local interstellar spectra and solar modulation

Cheng-Rui Zhu, Qiang Yuan, Da-Ming Wei
Submitted Wednesday 25 July 2018 @ 08:07:02 GMT
16 pages, 10 figures, 9 tables, accepted for publication in ApJ

The acceleration of cosmic ray particles and their propagation in the Milky Way and the heliosphere tangle with each other, leading to complexity and degeneracy of the modeling of Galactic cosmic rays (GCRs). The recent measurements of the GCR spectra by Voyager-1 from outside of the heliosphere gave a first direct observation of GCRs in the local interstellar (LIS) environment. Together with the high-precision data near the Earth taken by ACE and AMS-02, we derive the LIS spectra of Helium, Lithium, Beryllium, Boron, Carbon, and Oxygen nuclei from a few MeV/n to TeV/n, using a non-parameterization method. These LIS spectra are helpful in further studying the injection and propagation parameters of GCRs. The nearly 20 years of data recorded by ACE are used to determine the solar modulation parameters over the solar cycles 23 and 24, based on the force-field approximation. We find general agreements of the modulation potential with the results inferred from neutron monitors and other cosmic ray data.

[27] arXiv:1807.09454v1 [pdf, vox]

An Orbitrap-based laser desorption/ablation mass spectrometer designed for spaceflight

Ricardo Arevalo Jr., Laura Selliez, Christelle Briois, Nathalie Carrasco, Laurent Thirkell, Barnabé Cherville, Fabrice Colin, Bertrand Gaubicher, Benjamin Farcy, Xiang Li, Alexander Makarov
Submitted Wednesday 25 July 2018 @ 06:57:29 GMT

RATIONALE: The investigation of cryogenic planetary environments as potential harbors for extant life and/or contemporary sites of organic synthesis represents an emerging focal point in planetary exploration. Next generation instruments need to be capable of unambiguously determining elemental and/or molecular stoichiometry via highly accurate mass measurements and the separation of isobaric interferences. METHODS: An OrbitrapTM analyzer adapted for spaceflight (referred to as the CosmOrbitrap), coupled with a commercial pulsed UV laser source (266 nm), is shown to successfully characterize a variety of planetary analog samples via ultrahigh resolution laser desorption/ablation mass spectrometry. The materials analyzed in this study include: jarosite (a hydrous sulfate detected on Mars); magnesium sulfate (a potential component of the subsurface ocean on Europa); uracil (a nucleobase of RNA); and a variety of amino acids. RESULTS: The instrument configuration tested here enables: measurement of major elements and organic molecules with ultrahigh mass resolution (m/{\Delta}m higher than 120,000, FWHM); quantification of isotopic abundances with 1.0% (2{\sigma}) precision; and, identification of highly accurate masses within 3.2 ppm of absolute values. The analysis of a residue of a dilute solution of amino acids demonstrates the capacity to detect twelve amino acids in positive ion mode at concentrations as low as 1 pmol/mm2 while maintaining mass resolution and accuracy requirements. CONCLUSIONS: The CosmOrbitrap mass analyzer is highly sensitive and delivers mass resolution/accuracy unmatched by any instrument sent into orbit or launched into deep space. This prototype instrument, which maps to a spaceflight implementation, represents a missionenabling technology capable of advancing planetary exploration for decades to come.

[28] arXiv:1807.09442v1 [pdf, vox]

Optical identification of the binary companion to the millisecond PSR J2302+4442 with the Gran Telescopio Canarias

A. Yu. Kirichenko, S. V. Zharikov, D. A. Zyuzin, Yu. A. Shibanov, A. V. Karpova, S. Dai, A. Cabrera-Lavers
Submitted Wednesday 25 July 2018 @ 05:55:07 GMT
Accepted for publication in MNRAS

We report detection of the binary companion to the millisecond pulsar J2302+4442 based on the deep observations performed with the Gran Telescopio Canarias. The observations revealed an optical source with $r'$ = 23.33$\pm$0.02 and $i'$=23.08$\pm$0.02, whose position coincides with the pulsar radio position. By comparing the source colour and magnitudes with the white dwarf cooling predictions, we found that it likely represents a He or CO-core white dwarf and estimated its mass of 0.52$^{+0.25}_{-0.19​}$ M$_{\odot}$ and effective temperature of 6300$^{+1000}_{-800}​$ K. Combining our results with the radio timing measurements, we set constraints on the binary system inclination angle $i=73^{+6}_{-5}$ degrees and the pulsar mass $m_p=3.1^{+2.7}_{-2.​0}$ M$_{\odot}$.

[29] arXiv:1807.09412v1 [pdf, vox]

Impact of radio sources and cosmic infrared background on thermal Sunyaev-Zel'dovich - gravitational lensing cross correlation

Masato Shirasaki
Submitted Wednesday 25 July 2018 @ 01:52:11 GMT
8 pages, 5 figures. Comments welcome

Cross correlation with thermal Sunyaev-Zel'dovich (tSZ) effect in cosmic microwave background observation and weak gravitational lensing effect in galaxy imaging survey opens a new window on constraining matter contents in the Universe at redshift less than 1. In this paper, we study the impact of radio sources and cosmic infrared background (CIB) on observed tSZ-lensing correlation. Assuming the best-fit model of CIB by the Planck satellite, we estimate that the residual correlation of CIB with large-scale structures will be of an order of $2\%$ of expected tSZ-lensing correlation from intracluster medium in current lensing surveys. On the other hand, we find that correlation of lensing and radio sources can induce a negative correction for the observed tSZ-lensing correlation with a $\sim10\%$ level. This is originated from positive cross correlation with radio sources and lensing at $\sim100\, {\rm GHz}$ frequency, whereas tSZ-lensing correlation should show a negative value in temperature fluctuations at that frequency. We also show that the negative correction by radio-lensing correlation can solve the tension between recent measurements of tSZ-lensing correlation and an expected signal from ``universal'' gas pressure profile of nearby galaxy clusters, when the radio sources with flat-spectral index are assumed to populate massive cluster-sized dark matte halos. Our results indicate that minor source population in radio bands can play an important role in determining observed tSZ-lensing correlation at $<10$ arcmin.

[30] arXiv:1807.09409v1 [pdf, vox]

Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole

GRAVITY Collaboration, R. Abuter, A. Amorim, N. Anugu, M. Bauböck, M. Benisty, J. P. Berger, N. Blind, H. Bonnet, W. Brandner, A. Buron, C. Collin, F. Chapron, Y. Clénet, V. Coudé du Foresto, P. T. de Zeeuw, C. Deen, F. Delplancke-Ströbele, R. Dembet, J. Dexter, G. Duvert, A. Eckart, F. Eisenhauer, G. Finger, N. M. Förster Schreiber, P. Fédou, P. Garcia, R. Garcia Lopez, F. Gao, E. Gendron, R. Genzel, S. Gillessen, P. Gordo, M. Habibi, X. Haubois, M. Haug, F. Haußmann, Th. Henning, S. Hippler, M. Horrobin, Z. Hubert, N. Hubin, A. Jimenez Rosales, L. Jochum, L. Jocou, A. Kaufer, S. Kellner, S. Kendrew, P. Kervella, Y. Kok, M. Kulas, S. Lacour, V. Lapeyrère, B. Lazareff, J. -B. Le Bouquin, P. Léna, M. Lippa, R. Lenzen, A. Mérand, E. Müller, U. Neumann, T. Ott, L. Palanca, T. Paumard, L. Pasquini, K. Perraut, G. Perrin, O. Pfuhl, P. M. Plewa, S. Rabien, A. Ramírez, J. Ramos, C. Rau, G. Rodríguez-Coira, R. -R. Rohloff, G. Rousset, J. Sanchez-Bermudez, S. Scheithauer, M. Schöller, N. Schuler, J. Spyromilio, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, K. R. W. Tristram, F. Vincent, S. von Fellenberg, I. Wank, I. Waisberg, F. Widmann, E. Wieprecht, M. Wiest, E. Wiezorrek, J. Woillez, S. Yazici, D. Ziegler, G. Zins
Submitted Wednesday 25 July 2018 @ 01:36:07 GMT
Accepted for publication in A&A Letters, 29 June 2018, 10 pages, 6 figures, corresponding author: F. Eisenhauer <eisenhau@mpe.mpg.de​

The highly elliptical, 16-year-period orbit of the star S2 around the massive black hole candidate Sgr A* is a sensitive probe of the gravitational field in the Galactic centre. Near pericentre at 120 AU, ~1400 Schwarzschild radii, the star has an orbital speed of ~7650 km/s, such that the first-order effects of Special and General Relativity have now become detectable with current capabilities. Over the past 26 years, we have monitored the radial velocity and motion on the sky of S2, mainly with the SINFONI and NACO adaptive optics instruments on the ESO Very Large Telescope, and since 2016 and leading up to the pericentre approach in May 2018, with the four-telescope interferometric beam-combiner instrument GRAVITY. From data up to and including pericentre, we robustly detect the combined gravitational redshift and relativistic transverse Doppler effect for S2 of z ~ 200 km/s / c with different statistical analysis methods. When parameterising the post-Newtonian contribution from these effects by a factor f, with f = 0 and f = 1 corresponding to the Newtonian and general relativistic limits, respectively, we find from posterior fitting with different weighting schemes f = 0.90 +/- 0.09 (stat) +\- 0.15 (sys). The S2 data are inconsistent with pure Newtonian dynamics.

[31] arXiv:1807.09407v1 [pdf, vox]

Light variations due to the line-driven wind instability and wind blanketing in O stars

J. Krticka, A. Feldmeier
Submitted Wednesday 25 July 2018 @ 01:25:14 GMT
7 pages, accepted for publication in Astronomy & Astrophysics

A small fraction of the radiative flux emitted by hot stars is absorbed by their winds and redistributed towards longer wavelengths. This effect, which leads also to the heating of the stellar photosphere, is termed wind blanketing. For stars with variable winds, the effect of wind blanketing may lead to the photometric variability. We have studied the consequences of line driven wind instability and wind blanketing for the light variability of O stars. We combined the results of wind hydrodynamic simulations and of global wind models to predict the light variability of hot stars due to the wind blanketing and instability. The wind instability causes stochastic light variability with amplitude of the order of tens of millimagnitudes and a typical timescale of the order of hours for spatially coherent wind structure. The amplitude is of the order of millimagnitudes when assuming that the wind consists of large number of independent concentric cones. The variability with such amplitude is observable using present space borne photometers. We show that the simulated light curve is similar to the light curves of O stars obtained using BRITE and CoRoT satellites.

[32] arXiv:1807.09403v1 [pdf, vox]

Proton Acceleration in Weak Quasi-parallel Intracluster Shocks: Injection and Early Acceleration

Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang, Allard Jan van Marle
Submitted Wednesday 25 July 2018 @ 00:58:01 GMT
To appear in ApJ

Collisionless shocks with low sonic Mach numbers, $M_{\rm s} \lesssim 4$, are expected to accelerate cosmic ray (CR) protons via diffusive shock acceleration (DSA) in the intracluster medium (ICM). However, observational evidence for CR protons in the ICM has yet to be established. Performing particle-in-cell simulations, we study the injection of protons into DSA and the early development of a nonthermal particle population in weak shocks in high $\beta$ ($\approx 100$) plasmas. Reflection of incident protons, self-excitation of plasma waves via CR-driven instabilities, and multiple cycles of shock drift acceleration are essential to the early acceleration of CR protons in supercritical quasi-parallel shocks. We find that only in ICM shocks with $M_{\rm s} \gtrsim M_{\rm s}^*\approx 2.25$, a sufficient fraction of incoming protons are reflected by the overshoot in the shock electric potential and magnetic mirror at locally perpendicular magnetic fields, leading to efficient excitation of magnetic waves via CR streaming instabilities and the injection into the DSA process. Since a significant fraction of ICM shocks have $M_{\rm s} < M_{\rm s}^*$, CR proton acceleration in the ICM might be less efficient than previously expected. This may explain why the diffuse gamma-ray emission from galaxy clusters due to proton-proton collisions has not been detected so far.

[33] arXiv:1807.08757v2 [pdf, vox]

Connecting the X-ray properties of weak-line and typical quasars: testing for a geometrically thick accretion disk

Qingling Ni, W. N. Brandt, B. Luo, P. B. Hall, Yue Shen, S. F. Anderson, R. M. Plotkin, Gordon T. Richards, D. P. Schneider, O. Shemmer, J. Wu
Submitted Wednesday 25 July 2018 @ 00:17:31 GMT
21 pages, 12 figures. Accepted for publication in MNRAS

We present X-ray and multiwavelength analyses of 32 weak emission-line quasars (WLQs) selected in a consistent and unbiased manner. New $Chandra$ 3.1-4.8 ks observations were obtained for 14 of these WLQs with C IV rest-frame equivalent widths (REWs) of 5-15 \r{A}, and these serve as an X-ray observational "bridge" between previously studied WLQs with C IV REW $\lesssim$ 5 \r{A} and more-typical quasars with C IV REW $\approx$ 15-100 \r{A}. We have identified and quantified a strong dependence of the fraction of X-ray weak quasars upon C IV REW; this fraction declines by a factor of $\approx 13$ (from $\approx 44$% to $\approx 3$%) for C IV REW ranging from 4-50 \r{A}, and the rate of decline appears particularly strong in the 10-20 \r{A} range. The dependence broadly supports the proposed "shielding" model for WLQs, in which a geometrically and optically thick inner accretion disk, expected for a quasar accreting at a high Eddington ratio, both prevents ionizing EUV/X-ray photons from reaching the high-ionization broad emission-line region and also sometimes blocks the line-of-sight to the central X-ray emitting region. This model is also supported by the hard average spectral shape of X-ray weak WLQs (with a power-law effective photon index of $\Gamma_{\rm eff}=1.19^{+0.56}_{-​0.45}$). Additionally, we have examined UV continuum/emission-l​ine properties that might trace X-ray weakness among WLQs, confirming that red UV continuum color is the most-effective tracer.

Submitted Tue, 24 Jul 2018

[34] arXiv:1807.09397v1 [pdf, vox]

Singularities of plane gravitational waves and their memory effects

Tongzheng Wang, Jared Fier, Bowen Li, Guoliang Lv, Zhaojun Wang, Yumei Wu, Anzhong Wang
Submitted Tuesday 24 July 2018 @ 23:50:17 GMT
revtex4-1, no figures and tables

Similar to the Schwarzschild coordinates for spherical black holes, the Baldwin, Jeffery and Rosen coordinates for plane gravitational waves are often singular, and extensions beyond such singularities are necessary, before studying asymptotic properties of such spacetimes. In this paper, we study the nature of the singularities and find that some of them actually represent real spacetime singularities, so they already represent the boundaries of such spacetimes and extensions beyond them are not needed. As a result, such spacetimes cannot be used to study their asymptotical properties, such as memory effects and soft graviton theorems.

[35] arXiv:1807.09385v1 [pdf, vox]

Atmospheric spectroscopy at Gale Crater on Mars

V. A. Oliveira e P. H. Mombelli
Submitted Tuesday 24 July 2018 @ 23:07:20 GMT
2 pages, 2 figures, conference paper

Currently, Mars is the celestial object with the biggest quantity of devices made by mankind. This fact explain the astronomical quantity of data available about this planet, which allows several studies in several lines of research. Here we present the result of a monograph in Space Geophysics, in a graduation in Geophysics, the data used were collected by the device PFS (Planetary Fourier Spectrometer) in the mission MEX (Mars Express) launched in 2006. The main aim was the verification of the existence of methane (CH 4 ) in a specific region in the atmosphere of the Red Planet. The target region, Gale Crater, is where the Rover Curiosity is right now. Therefore, the choice was because the strong evidence of liquid water in the past on this site, and because Curiosity has identified an unusual amount of methane in the local atmosphere.

[36] arXiv:1807.09383v1 [pdf, vox]

Dark Energy Spectroscopic Instrument (DESI) Fiber Positioner Thermal and Wind Disturbance Test

Kai Zhang, Joseph H. Silber, Henry D. Heetderks, Daniela Leitner, Michael Schubnell, Michael Levi, Gradey Wang, Kevin Fanning, Parker Fagrelius, Carl Dobson, Jessica Aguilar
Submitted Tuesday 24 July 2018 @ 23:05:07 GMT
SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. To achieve this goal, it is crucial to guarantee that fiber positioners work properly under the extremes of potential operating conditions, including the full range of temperatures, high speed wind disturbance etc. Thermal testing provides valuable insight into the functionality of the fiber positioners that can be used to help mitigate poor performance at extreme temperatures and wind disturbance test provide guidance to design of ventilation system. Here, we describe the thermal and wind disturbance tests for DESI fiber positioners and how the test results helped improve the robustness of the positioners.

[37] arXiv:1807.09378v1 [pdf, vox]

The Commissioning Instrument for the Dark Energy Spectroscopic Instrument

Ashley J. Ross, Paul Martini, Rebecca Coles, Mark Derwent, Klaus Honscheid, Thomas P. O'Brien, Dan Pappalardo, Suk Sien Tie, David Brooks, Michael Schubnell, Greg Tarle
Submitted Tuesday 24 July 2018 @ 22:31:18 GMT
Presented at SPIE June 2018; Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 1070280

We describe the design of the Commissioning Instrument for the Dark Energy Spectroscopic Instrument (DESI). DESI will obtain spectra over a 3 degree field of view using the 4-meter Mayall Telescope at Kitt Peak, AZ. In order to achieve the required image quality over this field of view, a new optical corrector is being installed at the Mayall Telescope. The Commissioning Instrument is designed to characterize the image quality of the new optical system. The Commissioning Instrument has five commercial cameras; one at the center of the focal surface and four near the periphery of the field and at the cardinal directions. There are also 22 illuminated fiducials, distributed throughout the focal surface, that will be used to test the system that will map between the DESI fiber positioners and celestial coordinates. We describe how the commissioning instrument will perform commissioning tasks for the DESI project and thereby eliminate risks.

[38] arXiv:1807.09371v1 [pdf, vox]

Fabrication of the DESI Corrector Lenses

Timothy N. Miller, Robert W. Besuner, Michael E. Levi, Michael Lampton, Patrick Jelinsky, Henry Heetderks, David J. Schlegel, Jerry Edelstein, Peter Doel, David Brooks, Stephen Kent, Gary Poczulp, Michael J. Sholl
Submitted Tuesday 24 July 2018 @ 21:56:39 GMT

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the DESI corrector optics, a series of six fused silica and borosilicate lenses. The lens diameters range from 0.8 to 1.1 meters, and their weights 84 to 237 kg. Most lens surfaces are spherical, and two are challenging 10th-order polynomial aspheres. The lenses have been successfully polished and treated with an antireflection coating at multiple subcontractors, and are now being integrated into the DESI corrector barrel assembly at University College London. We describe the final performance of the lenses in terms of their various parameters, including surface figure, homogeneity, and others, and compare their final performance against the demanding DESI corrector requirements. Also we describe the reoptimization of the lens spacing in their corrector barrel after their final measurements are known. Finally we assess the performance of the corrector as a whole, compared to early budgeted estimates.

[39] arXiv:1807.09366v1 [pdf, vox]

The DESI Instrument Control System: Status and Early Testing

Klaus Honscheid, Ann Elliott, Elizabeth Buckley-Geer, Bezhad Abreshi, Francisco Castender, Luiz daCosta, Stephen Kent, David Kirkby, Robert Marshall, Eric Neilsen, Riccardo Ogando, David Rabinowitz, Aaron roodman, Santiago Serrano, David Brooks, Michael Levi, Greg Tarle
Submitted Tuesday 24 July 2018 @ 21:39:18 GMT
SPIE Astronomical Telescopes + Instrumentation, Austin, TX (2018)

The Dark Energy Spectroscopic Instrument (DESI) is a new instrument currently under construction for the Mayall 4-m telescope at Kitt Peak National Observatory. It will consist of a wide-field optical corrector with a 3.2 degree diameter field of view, a focal plane with 5,000 robotically controlled fiber positioners and 10 fiber-fed broad-band spectrographs. The DESI Instrument Control System (ICS) coordinates fiber positioner operations, interfaces to the Mayall telescope control system, monitors operating conditions, reads out the 30 spectrograph CCDs and provides observer support and data quality monitoring. In this article, we summarize the ICS design, review the current status of the project and present results from a multi-stage test plan that was developed to ensure the system is fully operational by the time the instrument arrives at the observatory in 2019.

[40] arXiv:1807.09365v1 [pdf, vox]

New rotation period measurements for M dwarfs in the southern hemisphere: an abundance of slowly rotating, fully convective stars

Elisabeth R. Newton, Nicholas Mondrik, Jonathan Irwin, Jennifer G. Winters, David Charbonneau
Submitted Tuesday 24 July 2018 @ 21:35:34 GMT
Accepted to IOP Journals. Machine readable tables and additional figures are available in the published article or on request

Stellar rotation periods are valuable both for constraining models of angular momentum loss and for under- standing how magnetic features impact inferences of exoplanet parameters. Building on our previous work in the northern hemisphere, we have used long-term, ground-based photometric monitoring from the MEarth Observatory to measure 234 rotation periods for nearby, southern hemisphere M dwarfs. Notable examples include the exoplanet hosts GJ 1132, LHS 1140, and Proxima Centauri. We find excellent agreement between our data and K2 photometry for the overlapping subset. Amongst the sample of stars with the highest quality datasets, we recover periods in 66%; as the length of the dataset increases, our recovery rate approaches 100%. The longest rotation periods we detect are around 140 days, which we suggest represent the periods that are reached when M dwarfs are as old as the local thick disk (about 9 Gyr).

[41] arXiv:1807.09361v1 [pdf, vox]

Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3 class Flare Observed by Hinode/EIS

Vanessa Polito, Jaroslav Dudík, Jana Kašparová, Elena Dzifčáková, Katharine K. Reeves, Paola Testa, Bin Chen
Submitted Tuesday 24 July 2018 @ 21:17:40 GMT

We analyze the spectra of high temperature \fexxiv~lines observed by \emph{Hinode}/EIS during the impulsive phase of the X8.3--class flare on September 10, 2017. The line profiles are broad, show pronounced wings, and clearly depart from a single Gaussian shape. The lines can be well fitted with $\kappa$ distributions, with values of $\kappa$ varying between~$\approx$1.7 to 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy ($\approx$100--300 keV) HXR sources observed by \emph{RHESSI}, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of a non-thermal microwave sources with the \emph{Expanded Owens Valley Solar Array} (EOVSA) at and above the HXR looptop source. We also investigate the effect of taking into account $\kappa$ distributions in the temperature diagnostics based on the ratio of the \fexxiii~263.76~\AA~​and \fexxiv~255.1~\AA~EI​S lines. We found that these lines can be formed at much higher temperatures than expected (up to log($T$\,[K])\,$\app​rox$\,7.8), if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply non-thermal broadening in excess of ~200\,\kps. The non-thermal broadening related to HXR emission is better interpreted by turbulence rather than chromospheric evaporation.

[42] arXiv:1807.09354v1 [pdf, vox]

Reconciling the predictions of microlensing analysis with radial velocity measurements for OGLE-2011-BLG-0417 FOR OGLE-2011-BLG-0417

E. Bachelet, J. -P. Beaulieu, I. Boisse, A. Santerne, R. A. Street
Submitted Tuesday 24 July 2018 @ 21:06:47 GMT
ApJ accepted

Microlensing is able to reveal multiple body systems located several kilo-parsec away from the Earth. Since it does not require the measurement of light from the lens, microlensing is sensitive to a range of objects from free-floating planets to stellar black holes. But if the lens emits enough light, the microlensing model predictions can be tested with high-resolution imaging and/or radial velocity methods. Such follow-up was done for the microlensing event OGLE-2011-BLG-0417, which was expected to be a close by ($\le$ 1 kpc), low-mass ($\sim 0.8 M_\odot$) binary star with a period $P\sim 1.4$ yr. The spectroscopic follow-up observations conducted with the VLT did not measure any variation in the radial velocity, in strong contradiction with the published microlensing model. In the present work, we remodel this event and find a simpler model in agreement with all the available measurements, including the recent GAIA DR2 parallax constraints. We also present a new way to distinguish degenerate models by using the GAIA DR2 proper motions. This work stresses the importance of thorough microlensing modeling, especially with the horizon of the {\it WFIRST} and the {\it Euclid} microlensing space missions.

[43] arXiv:1807.09337v1 [pdf, vox]

Characterization of atmospheric turbulence for the Large Synoptic Survey Telescope

Claire-Alice Hébert, Bruce Macintosh, Patricia R. Burchat
Submitted Tuesday 24 July 2018 @ 20:29:07 GMT

One of the scientific goals of the Large Synoptic Survey Telescope (LSST) is to measure the evolution of dark energy by measuring subtle distortions of galaxy shapes due to weak gravitational lensing caused by the evolving dark matter distribution. Understanding the point spread function (PSF) for LSST is a crucial step to accurate measurements of weak gravitational lensing. Atmospheric contributions dominate the LSST PSF. Simulations of Kolmogorov turbulence models are commonly used to characterize and correct for these atmospheric effects. In order to validate these simulations, we compare the predicted atmospheric behavior to empirical data. The simulations are carried out in GalSim, an open-source software package for simulating images of astronomical objects and PSFs. Atmospheric simulations are run by generating large phase screens at varying altitude and evolving them over long time scales. We compare the turbulence strength and temporal behavior of atmospheres generated from simulations to those from reconstructed telemetry data from the Gemini Planet Imager (GPI). GPI captures a range of spatial frequencies by sampling the atmosphere with 18-cm subapertures. The LSST weak lensing analysis will measure correlations of galaxy ellipticity, requiring very accurate knowledge of the magnitude and correlations of PSF shape parameters. Following from the first analysis, we use simulations and sequential short exposure observations from the Differential Speckle Survey Instrument (DSSI) to study the behavior of PSF parameters - e.g., ellipticity and size - as a function of exposure time. These studies could help inform discussions of possible variable exposure times for LSST visits for example, to provide more uniform depth of visits.

[44] arXiv:1807.09336v1 [pdf, vox]

The Coordinated Radio and Infrared Survey for High-mass Star Formation. IV: A new radio selected sample of compact Galactic Planetary Nebulae

T. Irabor, M. G. Hoare, R. D. Oudmaijer, J. S. Urquhart, S. Kurtz, S. L. Lumsden, C. R. Purcell, A. A. Zijlstra, G. Umana
Submitted Tuesday 24 July 2018 @ 20:28:52 GMT

We present a new radio-selected sample of PNe from the CORNISH survey. This is a radio continuum survey of the inner Galactic plane covering Galactic longitude, $10^\circ <l< 65^\circ$ and latitude, $|b| < 1^\circ$ with a resolution of 1.5$^{''}$ and sensitivity better than 0.4 mJy/beam. The radio regime, being unbiased by dust extinction, allows for a more complete sample selection, especially towards the Galactic mid-plane. Visual inspection of the CORNISH data, in combination with data from multi-wavelength surveys of the Galactic plane, allowed the CORNISH team to identify 169 candidate PNe. Here, we explore the use of multi-wavelength diagnostic plots and analysis to verify and classify the candidate PNe. We present the multi-wavelength properties of this new PNe sample. We find 90 new PNe, of which 12 are newly discovered and 78 are newly classified as PN. A further 47 previously suspected PNe are confirmed as such from the analysis presented here and 24 known PNe are detected. Eight sources are classified as possible PNe or other source types. Our sample includes a young sub-sample, with physical diameters < 0.12 pc, brightness temperatures (> 1000 K) and located closer than 7 kpc. Within this sample is a water-maser PN with a spectral index of $-0.55\pm 0.08$, which indicates non-thermal radio emission. Such a radio-selected sample, unaffected by extinction, will be particularly useful to compare with population synthesis models and should contribute to the understanding of the formation and evolution of PNe.

[45] arXiv:1807.09330v1 [pdf, vox]

The Wide Field Monitor onboard the eXTP mission

M. Hernanz, S. Brandt, M. Feroci, P. Orleanski, A. Santangelo, S. Schanne, Xin Wu, J. in't Zand, S. N. Zhang, Y. P. Xu, E. Bozzo, Y. Evangelista, J. L. Gálvez, C. Tenzer, F. Zwart, F. J. Lu, S. Zhang, T. X. Chen, F. Ambrosino, A. Argan, E. Del Monte, C. Budtz-Jørgensen, N. Lund, P. Olsen, C. Mansanet, R. Campana, F. Fuschino, C. Labanti, A. Rachevski, A. Vacchi, G. Zampa, N. Zampa, I. Rashevskaya, P. Bellutti, G. Borghi, F. Ficorella, A. Picciotto, N. Zorzi, O. Limousin, A. Meuris, on behalf of the eXTP Consortium
Submitted Tuesday 24 July 2018 @ 20:18:25 GMT
16 pages, 15 figures, to appear in proceedings of SPIE, Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray

The eXTP (enhanced X-ray Timing and Polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS) and China National Space Administration (CNSA) currently performing an extended phase A study and proposed for a launch by 2025 in a low-earth orbit. The eXTP scientific payload envisages a suite of instruments (Spectroscopy Focusing Array, Polarimetry Focusing Array, Large Area Detector and Wide Field Monitor) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. A large European consortium is contributing to the eXTP study and it is expected to provide key hardware elements, including a Wide Field Monitor (WFM). The WFM instrument for eXTP is based on the design originally proposed for the LOFT mission within the ESA context. The eXTP/WFM envisages a wide field X-ray monitor system in the 2-50 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors. The WFM will consist of 3 pairs of coded mask cameras with a total combined Field of View (FoV) of 90x180 degrees at zero response and a source localization accuracy of ~1 arcmin. In this paper we provide an overview of the WFM instrument design, including new elements with respect to the earlier LOFT configuration, and anticipated performance.

[46] arXiv:1807.09315v1 [pdf, vox]

Ensemble Properties of the White Dwarf Population of the Old, Solar Metallicity Open Star Cluster Messier 67

Kurtis A. Williams, Paul A. Canton, A. Bellini, Michael Bolte, Kate H. R. Rubin, Alexandros Gianninas, Mukremin Kilic
Submitted Tuesday 24 July 2018 @ 19:31:51 GMT
20 pages, 9 figures. Accepted for publication in the Astrophysical Journal

White dwarfs are excellent forensic tools for studying end-of-life issues surrounding low- and intermediate-mass stars, and the old, solar-metallicity open star cluster Messier 67 is a proven laboratory for the study of stellar evolution for solar-type stars. In this paper, we present a detailed spectroscopic study of brighter (M_g < 12.4) white dwarfs in Messier 67, and, in combination with previously-published proper motion membership determinations, we identify a clean, representative sample of cluster white dwarfs, including 13 members with hydrogen-dominated atmospheres, at least one of which is a candidate double degenerate, and 5 members with helium-dominated atmospheres. Using this sample we test multiple predictions surrounding the final stages of stellar evolution in solar type stars. In particular, the stochasticity of the integrated mass lost by ~1.5 solar mass stars is less than 7% of the white dwarf remnant mass. We identify white dwarfs likely resulting from binary evolution, including at least one blue straggler remnant and two helium core white dwarfs. We observe no evidence of a significant population of helium core white dwarfs formed by enhanced mass loss on the red giant branch of the cluster. The distribution of white dwarf atmospheric compositions is fully consistent with that in the field, limiting proposed mechanisms for the suppression of helium atmosphere white dwarf formation in star clusters. In short, the white dwarf population of Messier 67 is fully consistent with basic predictions of single- and multiple-star stellar evolution theories for solar metallicity stars.

[47] arXiv:1807.09311v1 [pdf, vox]

A large accretion disk of extreme eccentricity in the TDE ASASSN-14li

R. Cao, F. K. Liu, Z. Q. Zhou, S. Komossa, L. C. Ho
Submitted Tuesday 24 July 2018 @ 19:09:25 GMT
10 pages, 8 figures, accepted for publication in the MNRAS

In the canonical model for tidal disruption events (TDEs), the stellar debris circularizes quickly to form an accretion disk of size about twice the orbital pericenter of the star. Most TDEs and candidates discovered in the optical/UV have broad optical emission lines with complex and diverse profiles of puzzling origin. Liu et al. recently developed a relativistic elliptical disk model of constant eccentricity in radius for the broad optical emission lines of TDEs and well reproduced the double-peaked line profiles of the TDE candidate PTF09djl with a large and extremely eccentric accretion disk. In this paper, we show that the optical emission lines of the TDE ASASSN-14li with radically different profiles are well modelled with the relativistic elliptical disk model, too. The accretion disk of ASASSN-14li has an eccentricity 0.97 and semimajor axis of 847 times the Schwarzschild radius (r_S) of the black hole (BH). It forms as the consequence of tidal disruption of a star passing by a massive BH with orbital pericenter 25r_S. The optical emission lines of ASASSN-14li are powered by an extended X-ray source of flat radial distribution overlapping the bulk of the accretion disk and the single-peaked asymmetric line profiles are mainly due to the orbital motion of the emitting matter within the disk plane of inclination about 26\degr and of pericenter orientation closely toward the observer. Our results suggest that modelling the complex line profiles is powerful in probing the structures of accretion disks and coronal X-ray sources in TDEs.

[48] arXiv:1807.09309v1 [pdf, vox]

Sensitivity to luminosity, centrifugal force, and boundary conditions in spherical shell convection

Petri J. Käpylä, Frederick A. Gent, Nigul Olspert, Maarit J. Käpylä, Axel Brandenburg
Submitted Tuesday 24 July 2018 @ 19:07:43 GMT
25 pages, 14 figures, submitted to GAFD Special issue on 'Physics and Algorithms of the Pencil Code'

We test the sensitivity of hydrodynamic and magnetohydrodynamic convection simulations with respect to Mach number, thermal and magnetic boundary conditions, and the centrifugal force. We find that varying the luminosity, which also controls the Mach number, has only a minor effect on the large-scale dynamics. A similar conclusion can also be drawn from the comparison of two formulations of the lower magnetic boundary condition with either vanishing electric field or current density. The centrifugal force has an effect on the solutions, but only if its magnitude with respect to acceleration due to gravity is by two orders of magnitude greater than in the Sun. Finally, we find that the parameterization of the photospheric physics, either by an explicit cooling term or enhanced radiative diffusion, is more important than the thermal boundary condition. In particular, runs with cooling tend to lead to more anisotropic convection and stronger deviations from the Taylor-Proudman state.

[49] arXiv:1807.09307v1 [pdf, vox]

The extended HeII$λ$4686 emission in the extremely metal-poor galaxy SBS0335-052E seen with MUSE

C. Kehrig, J. M. Vilchez, M. A. Guerrero, J. Iglesias-Paramo, L. K. Hunt, S. Duarte Puertas, G. Ramos-Larios
Submitted Tuesday 24 July 2018 @ 19:00:39 GMT
Accepted for publication in MNRAS, 16 pages, 8 figures, 2 tables

SBS0335-052E, one of the most metal-poor (Z ~ 3-4% Z$_{\odot}$) HeII-emitter starbursts known in the nearby universe, is studied using optical VLT/MUSE spectroscopic and Chandra X-ray observations. We spatially resolved the spectral map of the nebular HeII$\lambda$4686 emission from which we derived for the first time the total HeII-ionizing energy budget of SBS0335-052E. The nebular HeII line is indicative of a quite hard ionizing spectrum with photon energies > 4 Ryd, and is observed to be more common at high-z than locally. Our study rules out a significant contribution from X-ray sources and shocks to the HeII photoionization budget, indicating that the He$^{+}$ excitation is mainly due to hot stellar continua. We discovered a new WR knot, but we also discard single WR stars as the main responsible for the HeII ionization. By comparing observations with current models, we found that the HeII-ionization budget of SBS0335-052E can only be produced by either single, rotating metal-free stars or a binary population with Z ~ 10$^{-5}$ and a 'top-heavy' IMF. This discrepancy between the metallicity of such stars and that of the HII regions in SBS0335-052E is similar to results obtained by Kehrig et al. (2015) for the very metal-deficient HeII-emitting galaxy IZw18. These results suggest that the HeII ionization is still beyond the capabilities of state-of-the-art models. Extremely metal-poor, high-ionizing starbursts in the local universe, like SBS0335-052E, provide unique laboratories for exploring in detail the extreme conditions likely prevailing in the reionization era.

[50] arXiv:1807.09297v1 [pdf, vox]

ALIOLI: Adaptive and Lucky Imaging Optics Lightweight Instrument

Sergio Velasco, Roberto L. López, Alejandro Oscoz, Carlos Colodro-Conde
Submitted Tuesday 24 July 2018 @ 18:28:25 GMT
4 pages, 5 figures, conference

As a consequence of the evolution in the design and of the modularity of its components, AOLI for the William Herschel Telescope (WHT 4.2m) is much smaller and more efficient than its previous designs. This success has leaded us to plan to condense it even more to get a portable and easy to integrate system, ALIOLI (Adaptive and Lucky Imaging Optics Lightweight Instrument). It consists of a DM+WFS module with a lucky imaging science camera attached. ALIOLI is an AO instrument for the 1-2m class telescopes which will also be used as on-sky testbench for AO developments. Here we describe the setup to be installed at the 1.5m Telescopio Carlos S\'anchez (TCS) at the Spanish Observatorio del Teide (Tenerife, Canary Islands).

[51] arXiv:1807.09287v1 [pdf, vox]

Overview of the Dark Energy Spectroscopic Instrument

Paul Martini, Stephen Bailey, Robert W. Besuner, David Brooks, Peter Doel, Jerry Edelstein, Daniel Eisenstein, Brenna Flaugher, Gaston Gutierrez, Stewart E. Harris, Klaus Honscheid, Patrick Jelinsky, Richard Joyce, Stephen Kent, Michael Levi, Francisco Prada, Claire Poppett, David Rabinowitz, Constance Rockosi, Laia Cardiel Sas, David J. Schlegel, Michael Schubnell, Ray Sharples, Joseph H. Silber, David Sprayberry, Risa Wechsler
Submitted Tuesday 24 July 2018 @ 18:03:52 GMT
11 pages, 4 figures

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project.

[52] arXiv:1807.09284v1 [pdf, vox]

The stellar populations of the central region of M31

R. P. Saglia, M. Opitsch, M. H. Fabricius, R. Bender, M. Blana, O. Gerhard
Submitted Tuesday 24 July 2018 @ 18:00:17 GMT
Accepted for publication in A&A

We continue the analysis of the dataset of our spectroscopic observation campaign of M31, by deriving simple stellar population properties (age metallicity and alpha-elements overabundance) from the measurement of Lick/IDS absorption line indices. We describe their two-dimensional maps taking into account the dust distribution in M31. 80\% of the values of our age measurements are larger than 10 Gyr. The central 100 arcsec of M31 are dominated by the stars of the classical bulge of M31. They are old (11-13 Gyr), metal-rich (as high as [Z/H]~0.35 dex) at the center with a negative gradient outwards and enhanced in alpha-elements ([alpha/Fe]~ 0.28+- 0.01 dex). The bar stands out in the metallicity map, where an almost solar value of [Z/H] (~0.02+-0.01 dex) with no gradient is observed along the bar position angle (55.7 deg) out to 600 arcsec from the center. In contrast, no signature of the bar is seen in the age and [alpha/Fe] maps, that are approximately axisymmetric, delivering a mean age and overabundance for the bar and the boxy-peanut bulge of 10-13 Gyr and 0.25-0.27 dex, respectively. The boxy/peanut-bulge has almost solar metallicity (-0.04+- 0.01 dex). The mass-to-light ratio of the three components is approximately constant at M/LV ~ 4.4-4.7 Msol/Lsol. The disk component at larger distances is made of a mixture of stars, as young as 3-4 Gyr, with solar metallicity and smaller M/LV (~3+-0.1 Msol/Lsol). We propose a two-phase formation scenario for the inner region of M31, where most of the stars of the classical bulge come into place together with a proto-disk, where a bar develops and quickly transforms it into a boxy-peanut bulge. Star formation continues in the bulge region, producing stars younger than 10 Gyr, in particular along the bar, enhancing its metallicity. The disk component appears to build up on longer time-scales.

[53] arXiv:1807.09283v1 [pdf, vox]

DESI Commissioning Instrument Metrology

Rebecca A. Coles, David Brooks, Mark Derwent, Paul Martini, Thomas O'Brien, Ashley Ross, Suk Sien Tie
Submitted Tuesday 24 July 2018 @ 18:00:16 GMT

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the methods and results for the commissioning instrument metrology program. The primary goals of this program are to calculate the transformations and further develop the systems that will place fibers within 5um RMS of the target positions. We will use the commissioning instrument metrology program to measure the absolute three axis Cartesian coordinates of the five CCDs and 22 illuminated fiducials on the commissioning instrument.

[54] arXiv:1807.09282v1 [pdf, vox]

Heating of the Intergalactic Medium by Hydrogen Reionization

Anson D'Aloisio, Matthew McQuinn, Oliver Maupin, Frederick B. Davies, Hy Trac, Spencer Fuller, Phoebe R. Upton Sanderbeck
Submitted Tuesday 24 July 2018 @ 18:00:11 GMT
Submitted to ApJ

During reionization, the intergalactic medium is heated impulsively by supersonic ionization fronts (I-fronts). The peak gas temperatures behind the I-fronts, $T_\mathrm{reion}$, are a key uncertainty in models of the thermal history after reionization. Here we use high-resolution radiative transfer simulations to study the parameter space of $T_\mathrm{reion}$. We show that $T_\mathrm{reion}$ is only mildly sensitive to the spectrum of incident radiation over most of the parameter space, with temperatures set primarily by I-front speeds. We also explore what current models of reionization predict for $T_\mathrm{reion}$ by measuring I-front speeds in cosmological radiative transfer simulations. We find that the post-I-front temperatures evolve toward hotter values as reionization progresses. Temperatures of $T_\mathrm{reion} = 17,000-22,000$ K are typical during the first half of reionization, but $T_\mathrm{reion} = 25,000 - 30,000$ K may be achieved near the end of this process if I-front speeds reach $\sim10^4$ km/s as found in our simulations. Shorter reionization epochs lead to hotter $T_\mathrm{reion}$. We discuss implications for $z>5$ Ly$\alpha$ forest observations, which potentially include sight lines through hot, recently reionized patches of the Universe. Interpolation tables from our parameter space study are made publicly available, along with a simple fit for the dependence of $T_\mathrm{reion}$ on the I-front speed.

[55] arXiv:1807.09281v1 [pdf, vox]

Intermediate-Mass Ratio Inspirals in Galactic Nuclei

Giacomo Fragione, Nathan Leigh
Submitted Tuesday 24 July 2018 @ 18:00:09 GMT
8 pages, 5 figures, 1 Table

In this paper, we study the secular dynamical evolution of binaries composed of intermediate-mass and stellar-mass black holes (IMBHs and SBHs, respectively) in orbit about a central super-massive black hole (SMBH) in galactic nuclei. Such BH triplets could form via the inspiral of globular clusters toward galactic nuclei due to dynamical friction, or even major/minor galaxy mergers. We perform, for reasonable initial conditions that we justify, sophisticated $N$-body simulations that include both regularization and Post-Newtonian corrections. We find that mass segregation combined with Kozai-Lidov oscillations induced by the primary SMBH can effectively merge IMBH-SBH binaries on time-scales much shorter than gravitational wave emission alone. Moreover, the rate of such extreme mass ratio inspirals could be high ($\sim 1\ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$) in the local Universe, but these are expected to be associated with recent GC infall or major/minor mergers, making the observational signatures of such events (e.g., tidal debris) good diagnostics for searching for SMBH-IMBH-SBH mergers. A small fraction could also be associated with tidal disruption events by the IMBH-SBH during inspiral.

[56] arXiv:1807.09280v1 [pdf, vox]

Role of stable modes in driven shear-flow turbulence

A. E. Fraser, M. J. Pueschel, P. W. Terry, E. G. Zweibel
Submitted Tuesday 24 July 2018 @ 18:00:06 GMT
34 pages pre-print format, 13 figures, submitted to Physics of Plasmas

A linearly unstable, sinusoidal $E \times B$ shear flow is examined in the gyrokinetic framework in both the linear and nonlinear regimes. In the linear regime, it is shown that the eigenmode spectrum is nearly identical to hydrodynamic shear flows, with a conjugate stable mode found at every unstable wavenumber. In the nonlinear regime, turbulent saturation of the instability is examined with and without the inclusion of a driving term that prevents nonlinear flattening of the mean flow, and a scale-independent radiative damping term that suppresses the excitation of conjugate stable modes. A simple fluid model for how momentum transport and partial flattening of the mean flow scale with the driving term is constructed, from which it is shown that, except at high radiative damping, stable modes play an important role in the turbulent state and yield significantly improved quantitative predictions when compared with corresponding models neglecting stable modes.

[57] arXiv:1807.09279v1 [pdf, vox]

Column Density Profiles of Cold Clouds Driven by Galactic Outflows

J'Neil Cottle, Evan Scannapieco, Marcus Bruggen
Submitted Tuesday 24 July 2018 @ 18:00:04 GMT
16 pages, 6 figures, accepted for publication in ApJ

Absorption line studies are essential to understanding the origin, nature, and impact of starburst-driven galactic outflows. Such studies have revealed a multiphase medium with a number of poorly-understood features leading to a need to study the ionization mechanism of this gas. To better interpret these observations, we make use of a suite of adaptive mesh refinement hydrodynamic simulations of cold, atomic clouds driven by hot, supersonic outflows, including the effect of radiative cooling, thermal conduction, and an ionizing background characteristic of a starbursting galaxy. Using a new analysis tool, Trident, we estimate the equilibrium column density distributions for ten different ions: H I, Mg II, C II, C III, C IV, Si III, Si IV, N V, O VI, and Ne VIII. These are fit to model profiles with two parameters describing the maximum column density and coverage, and for each ion we provide a table of these fit parameters, along with average velocities and line widths. Our results are most sensitive to Mach number and conduction efficiency, with higher Mach numbers and more efficient conduction leading to more compact, high column density clouds. We use our results to interpret down-the-barrel observations of outflows and find that the adopted ionization equilibrium model overpredicts column densities of ions such as Si IV and does not adequately capture the observed trends for N V and O VI, implying the presence of strong non equilibrium ionization effects.

[58] arXiv:1807.09277v1 [pdf, vox]

Spectroscopic investigation of a reionized galaxy overdensity at z=7

M. Castellano, L. Pentericci, E. Vanzella, F. Marchi, A. Fontana, P. Dayal, A. Ferrara, A. Hutter, S. Carniani, S. Cristiani, M. Dickinson, S. Gallerani, E. Giallongo, M. Giavalisco, A. Grazian, R. Maiolino, E. Merlin, D. Paris, S. Pilo, P. Santini
Submitted Tuesday 24 July 2018 @ 18:00:02 GMT
Accepted for publication in The Astrophysical Journal Letters. 6 pages, 3 figures

We present deep spectroscopic follow-up observations of the Bremer Deep Field (BDF) where the two $z\sim$7 bright Ly$\alpha$ emitters (LAE) BDF521 and BDF3299 were previously discovered by Vanzella et al. (2011) and where a factor of $\sim$3-4 overdensity of faint LBGs has been found by Castellano et al. (2016). We confirm a new bright Ly$\alpha$ emitter, BDF2195, at the same redshift of BDF521, $z=7.008$, and at only $\sim$90 kpc physical distance from it, confirming that the BDF area is likely an overdense, reionized region. A quantitative assessment of the Ly$\alpha$ fraction shows that the number of detected bright emitters is much higher than the average found at z$\sim$7, suggesting a high Ly$\alpha$ transmission through the inter-galactic medium (IGM). However, the line visibility from fainter galaxies is at odds with this finding, since no Ly$\alpha$ emission is found in any of the observed candidates with $M_{UV}>$-20.25. This discrepancy can be understood either if some mechanism prevents Ly$\alpha$ emission from fainter galaxies within the ionized bubbles from reaching the observer, or if faint galaxies are located outside the reionized area and bright LAEs are solely responsible for the creation of their own HII regions. A thorough assessment of the nature of the BDF region and of its sources of re-ionizing radiation will be made possible by JWST spectroscopic capabilities.

[59] arXiv:1807.09278v1 [pdf, vox]

Is every strong lens model unhappy in its own way? Uniform modelling of a sample of 12 quadruply+ imaged quasars

A. J. Shajib, S. Birrer, T. Treu, M. W. Auger, A. Agnello, T. Anguita, E. J. Buckley-Geer, J. H. H. Chan, T. E. Collett, F. Courbin, C. D. Fassnacht, J. Frieman, K. Issha, C. Lemon, H. Lin, P. J. Marshall, R. McMahon, A. More, V. Motta, M. Oguri, F. Ostrovski, C. E. Rusu, P. L. Schechter, T. Shanks, S. H. Suyu, G. Meylan, T. M. C. Abbott, S. Allam, J. Annis, S. Avila, E. Bertin, D. Brooks, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, C. E. Cunha, L. N. da Costa, J. De Vicente, S. Desai, P. Doel, B. Flaugher, P. Fosalba, J. García-Bellido, D. W. Gerdes, D. Gruen, R. A. Gruendl, G. Gutierrez, W. G. Hartley, D. L. Hollowood, B. Hoyle, D. J. James, K. Kuehn, N. Kuropatkin, O. Lahav, M. Lima, M. A. G. Maia, M. March, J. L. Marshall, P. Melchior, F. Menanteau, R. Miquel, A. A. Plazas, E. Sanchez, V. Scarpine, I. Sevilla-Noarbe, M. Smith, M. Soares-Santos, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, A. R. Walker
Submitted Tuesday 24 July 2018 @ 18:00:02 GMT
21 pages, 8 figures, 8 tables, submitted to MNRAS

Strong-gravitational lens systems with quadruply-imaged quasars (quads) are unique probes to address several fundamental problems in cosmology and astrophysics. Although they are intrinsically very rare, ongoing and planned wide-field deep-sky surveys are set to discover thousands of such systems in the next decade. It is thus paramount to devise a general framework to model strong-lens systems to cope with this large influx without being limited by expert investigator time. We propose such a general modelling framework (implemented with the publicly available software Lenstronomy) and apply it to uniformly model three band Hubble Space Telescope Wide Field Camera 3 images of 12 quads. This is the largest uniformly modelled sample of quads to date and paves the way for a variety of studies. To illustrate the scientific content of the sample, we investigate the alignment between the mass and light distribution in the deflectors. The position angles of these distributions are well-aligned, except when there is strong external shear. However, we find no correlation between the ellipticity of the light and mass distributions. We also show that the observed flux-ratios between the images depart significantly from the predictions of simple smooth models. The departures are strongest in the bluest band, consistent with microlensing being the dominant cause in addition to millilensing. Future papers will exploit this rich dataset in combination with ground based spectroscopy and time delays to determine quantities such as the Hubble constant, the free streaming length of dark matter, and the normalization of the initial stellar mass function.

[60] arXiv:1807.09274v1 [pdf, vox]

The rise and fall of the UV upturn: $z=0.3,\ 0.55$ and $0.7$

Sadman Ali, Malcolm Bremer, Steven Phillipps, Roberto De Propris, H. H. Wills Physics Laboratory, University of Bristol, UK, FINCA, University of Turku, Finland
Submitted Tuesday 24 July 2018 @ 18:00:01 GMT
MNRAS accepted

We have analysed the strength of the UV upturn in red sequence galaxies with luminosities reaching to below the $L^*$ point within four clusters at $z$ = 0.3, 0.55 \& 0.7. We find that the incidence and strength of the upturn remains constant up to $z=0.55$. In comparison, the prevalence and strength of the UV upturn is significantly diminished in the $z=0.7$ cluster, implying that the stellar population responsible for the upturn in a typical red sequence galaxy is only just developing at this redshift and is essentially fully-developed by $\sim 1$ Gyr later. Of all the mainstream models that seek to explain the UV upturn phenomenon, it is those that generate the upturn through the presence of a Helium-enhanced stellar subpopulation on the (hot) horizontal branch that are most consistent with this behaviour. The epoch ($z=0.7$) where the stars responsible for the upturn first evolve from the red giant branch places constraints on their age and chemical abundances. By comparing our results with the prediction made by the YEPS Helium-enhanced spectrophotometic models, we find that a solar metallicity sub-population that displays a consistent upturn between $0<z<0.55$ but then fades by $z=0.7$ would require a Helium abundance of $Y\geqslant0.45$, if formed at $z_f\sim4$. Later formation redshifts and/or higher metallicity would further increase the Helium enhancement required to produce the observed upturn in these clusters and vice versa.

[61] arXiv:1807.09276v1 [pdf, vox]

The mass-metallicity relation of high-z type-2 active galactic nuclei

Kenta Matsuoka, Tohru Nagao, Alessandro Marconi, Roberto Maiolino, Filippo Mannucci, Giovanni Cresci, Koki Terao, Hiroyuki Ikeda
Submitted Tuesday 24 July 2018 @ 18:00:01 GMT
7 pages, 4 figures, accepted for publication in A&A

The mass-metallicity relation (MZR) of type-2 active galactic nuclei (AGNs) at 1.2 < z < 4.0 is investigated by using high-z radio galaxies (HzRGs) and X-ray selected radio-quiet AGNs. We combine new rest-frame ultraviolet (UV) spectra of two radio-quiet type-2 AGNs obtained with FOCAS on the Subaru Telescope with existing rest-frame UV emission lines, i.e., CIV1549, HeII1640, and CIII]1909, of a sample of 16 HzRGs and 6 additional X-ray selected type-2 AGNs, whose host stellar masses have been estimated in literature. We divided our sample in three stellar mass bins and calculated averaged emission-line flux ratios of CIV1549/HeII1640 and CIII]1909/CIV1549. Comparing observed emission-line flux ratios with photoionization model predictions, we estimated narrow line region (NLR) metallicities for each mass bin. We found that there is a positive correlation between NLR metallicities and stellar masses of type-2 AGNs at z ~ 3. This is the first indication that AGN metallicities are related to their hosts, i.e., stellar mass. Since NLR metallicities and stellar masses follow a similar relation as the MZR in star-forming galaxies at similar redshifts, our results indicate that NLR metallicities are related to those of the host galaxies. This study highlights the importance of considering lower-mass X-ray selected AGNs in addition to radio galaxies to explore the metallicity properties of NLRs at high redshift.

[62] arXiv:1807.09272v1 [pdf, vox]

Confirmation of the link between central star binarity and extreme abundance discrepancy factors in planetary nebulae

R. Wesson, D. Jones, J. Garcia-Rojas, H. M. J. Boffin, R. L. M. Corradi
Submitted Tuesday 24 July 2018 @ 18:00:00 GMT
27 pages, 22 figures. Accepted for publication in MNRAS

It has recently been noted that there seems to be a strong correlation between planetary nebulae with close binary central stars, and highly enhanced recombination line abundances. We present new deep spectra of seven objects known to have close binary central stars, and find that the heavy element abundances derived from recombination lines exceed those from collisionally excited lines by factors of 5-95, placing several of these nebulae among the most extreme known abundance discrepancies. This study nearly doubles the number of nebulae known to have a binary central star and an extreme abundance discrepancy. A statistical analysis of all nebulae with measured recombination line abundances reveals no link between central star surface chemistry and nebular abundance discrepancy, but a clear link between binarity and the abundance discrepancy, as well as an anti-correlation between abundance discrepancies and nebular electron densities: all nebulae with a binary central star with a period of less than 1.15 days have an abundance discrepancy factor exceeding 10, and an electron density less than $\sim$1000 cm$^{-3}$; those with longer period binaries have abundance discrepancy factors less than 10 and much higher electron densities. We find that [O~{\sc ii}] density diagnostic lines can be strongly enhanced by recombination excitation, while [S~{\sc ii}] lines are not. These findings give weight to the idea that extreme abundance discrepancies are caused by a nova-like eruption from the central star system, occurring soon after the common-envelope phase, which ejects material depleted in hydrogen, and enhanced in CNONe but not in third-row elements.

[63] arXiv:1807.09273v1 [pdf, vox]

Statistical challenges in the search for dark matter

Sara Algeri, Melissa van Beekveld, Nassim Bozorgnia, Alyson Brooks, J. Alberto Casas, Jessi Cisewski-Kehe, Francis-Yan Cyr-Racine, Thomas D. P. Edwards, Fabio Iocco, Bradley J. Kavanagh, Judita Mamužić, Siddharth Mishra-Sharma, Wolfgang Rau, Roberto Ruiz de Austri, Benjamin R. Safdi, Pat Scott, Tracy R. Slatyer, Yue-Lin Sming Tsai, Aaron C. Vincent, Christoph Weniger, Jennifer Rittenhouse West, Robert L. Wolpert
Submitted Tuesday 24 July 2018 @ 18:00:00 GMT
32 pages, 8 figures, 331 references

The search for the particle nature of dark matter has given rise to a number of experimental, theoretical and statistical challenges. Here, we report on a number of these statistical challenges and new techniques to address them, as discussed in the DMStat workshop held Feb 26 - Mar 3 2018 at the Banff International Research Station for Mathematical Innovation and Discovery (BIRS) in Banff, Alberta.

[64] arXiv:1807.09263v1 [pdf, vox]

Self-Generated Cosmic-Ray Confinement in TeV Halos: Implications for TeV Gamma-Ray Emission and the Positron Excess

Carmelo Evoli, Tim Linden, Giovanni Morlino
Submitted Tuesday 24 July 2018 @ 17:59:59 GMT
10 pages, 3 figures, To Be Submitted

Recent observations have detected extended TeV gamma-ray emission surrounding young and middle-aged pulsars. The morphology of these "TeV halos" requires cosmic-ray diffusion to be locally suppressed by a factor of ~100-1000 compared to the typical interstellar medium. No model currently explains this suppression. We show that cosmic-ray self-confinement can significantly inhibit diffusion near pulsars. The steep cosmic-ray gradient generates Alfven waves that resonantly scatter the same cosmic-ray population, suppressing diffusion within ~20 pc of pulsars younger than ~100 kyr. In this model, TeV halos evolve through two phases, a growth phase where Alfven waves are resonantly generated and cosmic-ray diffusion becomes increasingly suppressed, and a subsequent relaxation phase where the diffusion coefficient returns to the standard interstellar value. Intriguingly, cosmic-rays are not strongly confined early in the TeV halo evolution, allowing a significant fraction of injected e+e- to escape. If these e+e- also escape from the surrounding supernova remnant, they would provide a natural explanation for the positron excess observed by PAMELA and AMS-02. Recently created TeV cosmic-rays are confined in the TeV halo, matching observations by HAWC and H.E.S.S. While our default model relaxes too rapidly to explain the confinement of TeV cosmic rays around mature pulsars, such as Geminga, models utilizing a Kraichnan turbulence spectrum experience much slower relaxation. Thus, observations of TeV halos around mature pulsars may provide a probe into our understanding of interstellar turbulence.

[65] arXiv:1807.09262v1 [pdf, vox]

The low mass population of the Vela OB2 association from Gaia

Joseph J. Armstrong, Nicholas J. Wright, R. D. Jeffries
Submitted Tuesday 24 July 2018 @ 17:57:49 GMT
6 pages, 4 figures, accepted for publication in MNRAS

The first Gaia Data Release presents an opportunity to characterise the low-mass population of OB associations, providing larger statistical samples and better constraints on the formation and evolution of clusters and associations. Using previously known low mass members in a small region of Vela OB2 we have designed selection criteria that combine Gaia and 2MASS photometry, independently of any astrometric information, to identify low-mass pre-main-sequence (PMS) stars over the wider association area. Our method picks out the known clusters of young stars around $\gamma^2$ Velorum and NGC-2547, but also identifies other over-densities that may represent previously unknown clusters. There are clear differences in the spatial distributions of the low-mass and the high-mass OB populations, suggesting either that the structure and dynamics of these populations has evolved separately or that the initial mass function can vary considerably on small scales within a single association.

[66] arXiv:1807.09253v1 [pdf, vox]

The Snowball Chamber: Neutron-Induced Nucleation in Supercooled Water

M. Szydagis, C. Knight, C. Levy
Submitted Tuesday 24 July 2018 @ 17:49:28 GMT
8 pages, 5 figures, and 2 tables

The cloud and bubble chambers have been used historically for particle detection, capitalizing on supersaturation and superheating respectively. Here we present the snowball chamber, which utilizes supercooled liquid. In our prototype, an incoming particle triggers crystallization of purified water. We demonstrate water is supercooled for a significantly shorter time with respect to control data in the presence of AmBe and $^{252}$Cf neutron sources. A greater number of multiple nucleation sites are observed as well in neutron calibration data, as in a PICO-style bubble chamber. Similarly, gamma calibration data indicate a high degree of insensitivity to electron recoils inducing the phase transition, making this detector potentially ideal for dark matter searches seeking nuclear recoil alone, while muon veto coincidence with crystallization indicates that at least the hadronic component of cosmic-ray showers triggers nucleation. We explore the possibility of using this new technology for WIMP and low-mass dark matter searches, and conclude with a discussion of the interdisciplinary implications of radiation-induced freezing of water for chemistry, biology, and atmospheric sciences.

[67] arXiv:1807.09241v1 [pdf, vox]

Dark Energy in light of Multi-Messenger Gravitational-Wave astronomy

Jose María Ezquiaga, Miguel Zumalacárregui
Submitted Tuesday 24 July 2018 @ 17:24:45 GMT
28 pages, 13 figures, 1 table. Comments welcome

Gravitational waves (GWs) provide a new tool to probe the nature of dark energy (DE) and the fundamental properties of gravity. We review the different ways in which GWs can be used to test gravity and models for late-time cosmic acceleration. Lagrangian-based gravitational theories beyond general relativity (GR) are classified into those breaking fundamental assumptions, containing additional fields and massive graviton(s). In addition to Lagrangian based theories we present the effective theory of DE and the $\mu$-$\Sigma$ parametrization as general descriptions of cosmological gravity. Multi-messenger GW detections can be used to measure the cosmological expansion (standard sirens), providing an independent test of the DE equation of state and measuring the Hubble parameter. Several key tests of gravity involve the cosmological propagation of GWs, including anomalous GW speed, massive graviton excitations, Lorentz violating dispersion relation, modified GW luminosity distance and additional polarizations, which may also induce GW oscillations. We summarize present constraints and their impact on DE models, including those arising from the binary neutron star merger GW170817. Upgrades of LIGO-Virgo detectors to design sensitivity and the next generation facilities such as LISA or Einstein Telescope will significantly improve these constraints in the next two decades.

[68] arXiv:1807.09240v1 [pdf, vox]

Reliable detection and characterization of low-frequency polarized sources in the LOFAR M51 field

A. Neld, C. Horellou, D. D. Mulcahy, R. Beck, S. Bourke, T. D. Carozzi, K. T. Chyży, J. E. Conway, J. S. Farnes, A. Fletcher, M. Haverkorn, G. Heald, A. Horneffer, B. Nikiel-Wroczyński, R. Paladino, S. S. Sridhar, C. L. Van Eck
Submitted Tuesday 24 July 2018 @ 17:23:21 GMT
17 pages, 11 figures, accepted for publication in A&A

The new generation of broad-band radio continuum surveys will provide large data sets with polarization information. New algorithms need to be developed to extract reliable catalogs of linearly polarized sources that can be used to characterize those sources and produce a dense rotation measure (RM) grid to probe magneto-ionized structures along the line of sight via Faraday rotation. The aim of the paper is to develop a computationally efficient and rigorously defined source-finding algorithm for linearly polarized sources. We used a calibrated data set from the LOw Frequency ARray (LOFAR) at 150 MHz centered on the nearby galaxy M51 to search for polarized background sources. With a new imaging software, we re-imaged the field at a resolution of 18''x15'' and cataloged a total of about 3000 continuum sources within 2.5 degrees of the center of M51. We made small Stokes Q and U images centered on each source brighter than 100 mJy in total intensity (201 sources) and used RM synthesis to create corresponding Faraday cubes that were analyzed individually. For each source, the noise distribution function was determined from a subset of measurements at high Faraday depths where no polarization is expected; the peaks in polarized intensity in the Faraday spectrum were identified and the p-value of each source was calculated. Finally, the false discovery rate method was applied to the list of p-values to produce a list of polarized sources and quantify the reliability of the detections. We also analyzed sources fainter than 100 mJy but that were reported as polarized in the literature at at least another radio frequency. Of the 201 sources that were searched for polarization, 6 polarized sources were detected confidently (with a false discovery rate of 5 percent). This corresponds to a number density of 1 polarized source per 3.3 square degrees, or 0.3 source/square degree. [Abridged]

[69] arXiv:1807.09239v1 [pdf, vox]

A fast and exact $w$-stacking and $w$-projection hybrid algorithm for wide-field interferometric imaging

Luke Pratley, Melanie Johnston-Hollitt, Jason D. McEwen
Submitted Tuesday 24 July 2018 @ 17:22:57 GMT
6 Figures, 19 Pages. Submitted to ApJ

The standard wide-field imaging technique, the $w$-projection, allows correction for wide-fields of view for non-coplanar radio interferometric arrays. However, calculating exact corrections for each measurement has not been possible due to the amount of computation required at high resolution and with the large number of visibilities from current interferometers. The required accuracy and computational cost of these corrections is one of the largest unsolved challenges facing next generation radio interferometers such as the Square Kilometre Array. We show that the same calculation can be performed with a radially symmetric $w$-projection kernel, where we use one dimensional adaptive quadrature to calculate the resulting Hankel transform, decreasing the computation required for kernel generation by several orders of magnitude, whilst preserving the accuracy. We demonstrate the potential of our radially symmetric $w$-projection kernel via sparse image reconstruction, using the software package Purify. We develop an MPI distributed $w$-stacking and $w$-projection hybrid algorithm, where we apply exact $w$-term corrections for 100 million measurements with $w$-terms between $\pm 300$ wavelengths, for a $17^\circ$ field of view and image size of 4096 by 4096 pixels. The pre-computation and reconstruction took a total time of 35 minutes. Such a level of accuracy and scalability is not possible with standard $w$-projection kernel generation methods. This demonstrates that we can scale to the large number of measurements and large image sizes expected from next generation interferometers whilst still maintaining both speed and accuracy. This work is a critical development for resolving one of the biggest unsolved challenges in interferometry.

[70] arXiv:1807.09235v1 [pdf, vox]

The Impact of Spectroscopic Fibre Collisions on the Observed Angular Correlation Function

Yjan A. Gordon, Kevin A. Pimbblet, Matt S. Owers
Submitted Tuesday 24 July 2018 @ 17:07:31 GMT
Accepted for publication in Research Notes of the AAS, 3 pages, 1 figure

The design of some spectroscopic galaxy surveys is such that fibre collisions can affect the completeness of the survey. To quantify this effect, we compare the two-point correlation functions, $\omega(\theta)$, of two surveys with differing observational strategies. Fibre collisions are an accepted consequence of the design of the Sloan Digital Sky Survey's spectroscopic campaign (SDSS), whereas the Galaxy And Mass Assembly survey (GAMA) circumvents fibre-collisions by re-observing fields using different fibre configurations. We show that the correlation functions of these surveys diverge at scales smaller than the SDSS fibre collision limit, and that at separations smaller than $20''$ $\omega(\theta)_{\te​xt{GAMA}} > \omega(\theta)_{\tex​t{SDSS}}$ with $>4\sigma$ confidence.

[71] arXiv:1807.09195v1 [pdf, vox]

Constraints on Cosmology and Baryonic Feedback with the Deep Lens Survey Using Galaxy-Galaxy and Galaxy-Mass Power Spectra

Mijin Yoon, M. James Jee, J. Anthony Tyson, Samuel Schmidt, David Wittman, Ami Choi
Submitted Tuesday 24 July 2018 @ 15:49:13 GMT
Submitted to ApJ. Comments welcome

We present cosmological parameter measurements from the Deep Lens Survey (DLS) using galaxy-mass and galaxy-galaxy power spectra in the multipole range $\ell=250\sim2000$. We measure galaxy-galaxy power spectra from two lens bins centered at $z\sim0.27$ and $0.54$ and galaxy-mass power spectra by cross-correlating the positions of galaxies in these two lens bins with galaxy shapes in two source bins centered at $z\sim0.64$ and $1.1$. We marginalize over a baryonic feedback process using a single-parameter representation and a sum of neutrino masses, as well as photometric redshift and shear calibration systematic uncertainties. For a flat $\Lambda$CDM cosmology, we determine $S_8\equiv\sigma_8\s​qrt{\Omega_m/0.3}=0.​818^{+0.031}_{-0.039​}$, in good agreement with our previous DLS cosmic shear and the Planck Cosmic Microwave Background (CMB) measurements. Without the baryonic feedback marginalization, $S_8$ decreases by $\sim0.05$ because the dark matter-only power spectrum lacks the suppression at the highest $\ell$'s due to Active Galactic Nuclei (AGN) feedback. Together with the Planck CMB measurement, we constrain the baryonic feedback parameter to $A_{baryon}=1.07^{+0​.29}_{-0.37}$, which suggests an interesting possibility that the actual AGN feedback might be stronger than the recipe used in the OWLS simulations. The interpretation is limited by the validity of this one-parameter representation of the baryonic feedback effect.

[72] arXiv:1807.09178v1 [pdf, vox]

The XMM-Newton serendipitous survey. VIII: The first XMM-Newton serendipitous source catalogue from overlapping observations

I. Traulsen, A. D. Schwope, G. Lamer, J. Ballet, F. Carrera, M. Coriat, M. J. Freyberg, L. Michel, C. Motch, S. R. Rosen, N. Webb, M. T. Ceballos, F. Koliopanos, J. Kurpas, M. Page, M. G. Watson
Submitted Tuesday 24 July 2018 @ 15:27:15 GMT
Submitted to A&A. 26 pages

XMM-Newton has observed the X-ray sky since the beginning of 2000. The XMM-Newton Survey Science Centre Consortium has been publishing catalogues of X-ray and ultraviolet sources found serendipitously in the individual observations. This series is now augmented by a catalogue dedicated to X-ray sources detected in spatially overlapping XMM-Newton observations. This catalogue aims at exploring repeatedly observed sky regions. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate long-term flux variability directly through the source detection process. A new standardised strategy for simultaneous source detection on multiple observations is introduced. It is coded as a new task edetect_stack within the XMM-Newton Science Analysis System and used to compile a catalogue of sources from 434 stacks comprising 1,789 selected overlapping full-frame observations. The first stacked catalogue is called 3XMM-DR7s. It contains 71,951 unique sources with positions and source parameters like fluxes, hardness ratios, quality estimate, and information on inter-observation variability, which are directly derived from a simultaneous fit and calculated for the stack and for each contributing observation. More than 8,000 sources are new with respect to 3XMM-DR7. By stacked source detection, the parameters of repeatedly observed sources can be determined with higher accuracy than in the individual observations. It is more sensitive to faint sources and tends to produce fewer spurious detections. With this first catalogue we demonstrate the feasibility and benefit of the approach. It supplements the large data base of XMM-Newton detections by additional, in particular faint, sources and new variability information. In the future, it will be expanded to larger samples and continued within the series of serendipitous XMM-Newton source catalogues.

[73] arXiv:1807.09134v1 [pdf, vox]

Insights into the inner regions of the FU Orionis disc

Michal Siwak, Maciej Winiarski, Waldemar Ogloza, Marek Drozdz, Stanislaw Zola, Anthony F. J. Moffat, Grzegorz Stachowski, Slavek M. Rucinski, Chris Cameron, Jaymie M. Matthews, Werner W. Weiss, Rainer Kuschnig, Jason F. Rowe, David B. Guenther, Dimitar Sasselov
Submitted Tuesday 24 July 2018 @ 14:11:56 GMT
Accepted to A&A

Context. We investigate small-amplitude light variations in FU Ori occurring in timescales of days and weeks. Aims. We seek to determine the mechanisms that lead to these light changes. Methods. The visual light curve of FU Ori gathered by the MOST satellite continuously for 55 days in the 2013-2014 winter season and simultaneously obtained ground-based multi-colour data were compared with the results from a disc and star light synthesis model. Results. Hotspots on the star are not responsible for the majority of observed light variations. Instead, we found that the long periodic family of 10.5-11.4 d (presumably) quasi-periods showing light variations up to 0.07 mag may arise owing to the rotational revolution of disc inhomogeneities located between 16-20 solar radii. The same distance is obtained by assuming that these light variations arise because of a purely Keplerian revolution of these inhomogeneities for a stellar mass of 0.7 solar mass. The short-periodic (3-1.38 d) small amplitude (0.01 mag) light variations show a clear sign of period shortening, similar to what was discovered in the first MOST observations of FU Ori. Our data indicate that these short-periodic oscillations may arise because of changing visibility of plasma tongues (not included in our model), revolving in the magnetospheric gap and/or likely related hotspots as well. Conclusions. Results obtained for the long-periodic 10-11 d family of light variations appear to be roughly in line with the colour-period relation, which assumes that longer periods are produced by more external and cooler parts of the disc. Coordinated observations in a broad spectral range are still necessary to fully understand the nature of the short-periodic 1-3 d family of light variations and their period changes.

[74] arXiv:1807.09110v1 [pdf, vox]

Cold gas in a complete sample of group-dominant early-type galaxies

E. O'Sullivan, F. Combes, P. Salomé, L. P. David, A. Babul, J. M. Vrtilek, J. Lim, V. Olivares, S. Raychaudhury, G. Schellenberger
Submitted Tuesday 24 July 2018 @ 13:46:35 GMT
20 pages, 12 PDF figures, accepted by A&A

We present IRAM 30m and APEX telescope observations of CO(1-0) and CO(2-1) lines in 36 group-dominant early-type galaxies, completing our molecular gas survey of dominant galaxies in the Complete Local-volume Groups Sample. We detect CO emission in 12 of the galaxies at >4sigma significance, with molecular gas masses in the range 0.01-6x10^8 Msol, as well as CO in absorption in the non-dominant group member galaxy NGC 5354. In total 21 of the 53 CLoGS dominant galaxies are detected in CO and we confirm our previous findings that they have low star formation rates (0.01-1 Msol/yr) but short depletion times (<1Gyr) implying rapid replenishment of their gas reservoirs. Comparing molecular gas mass with radio luminosity, we find that a much higher fraction of our group-dominant galaxies (60+-16%) are AGN-dominated than is the case for the general population of ellipticals, but that there is no clear connection between radio luminosity and the molecular gas mass. Using data from the literature, we find that at least 27 of the 53 CLoGS dominant galaxies contain HI, comparable to the fraction of nearby non-cluster early type galaxies detected in HI and significantly higher that the fraction in the Virgo cluster. We see no correlation between the presence of an X-ray detected intra-group medium and molecular gas in the dominant galaxy, but find that the HI-richest galaxies are located in X-ray faint groups. Morphological data from the literature suggests the cold gas component most commonly takes the form of a disk, but many systems show evidence of galaxy-galaxy interactions, indicating that they may have acquired their gas through stripping or mergers. We provide improved molecular gas mass estimates for two galaxies previously identified as being in the centres of cooling flows, NGC 4636 and NGC 5846, and find that they are relatively molecular gas poor compared to our other detected systems.

[75] arXiv:1807.09100v1 [pdf, vox]

On the 2018 outburst of the accreting millisecond X-ray pulsar Swift J1756.9-2508 as seen with NICER

Peter Bult, Diego Altamirano, Zaven Arzoumanian, Deepto Chakrabarty, Keith C. Gendreau, Sebastien Guillot, Wynn C. G. Ho, Gaurava K. Jaisawal, Steven Lentine, Craig B. Markwardt, Son N. Ngo, John S. Pope, Paul. S. Ray, Maxine R. Saylor, Tod E. Strohmayer
Submitted Tuesday 24 July 2018 @ 13:28:31 GMT
9 pages, 4 figures, 2 tables. Accepted for publication in ApJ

We report on the coherent timing analysis of the 182 Hz accreting millisecond X-ray pulsar Swift J1756.9$-$2508 during its 2018 outburst as observed with the Neutron Star Interior Composition Explorer (NICER). Combining our NICER observations with Rossi X-ray Timing Explorer observations of the 2007 and 2009 outbursts, we also studied the long-term spin and orbital evolution of this source. We find that the binary system is well described by a constant orbital period model, with an upper limit on the orbital period derivative of $|\dot P_b| < 7.4\times 10^{-13}$ s s$^{-1}$. Additionally, we improve upon the source coordinates through astrometric analysis of the pulse arrival times, finding R.A. = $17^{\rm h}56^{\rm m}57.18^{\rm s}\pm0.08^{\rm s}$ and Decl. = $-25^{\circ}06'27.8'​'\pm3.5''$, while simultaneously measuring the long-term spin frequency derivative as $\dot\nu = -7.3\times 10^{-16}$ Hz s$^{-1}$. We briefly discuss the implications of these measurements in the context of the wider population of accreting millisecond pulsars.

[76] arXiv:1807.09080v1 [pdf, vox]

SKA-Athena Synergy White Paper

R. Cassano, R. Fender, C. Ferrari, A. Merloni, T. Akahori, H. Akamatsu, Y. Ascasibar, D. Ballantyne, G. Brunetti, E. Corbelli, J. Croston, I. Donnarumma, S. Ettori, R. Ferdman, L. Feretti, J. Forbrich, C. Gheller, G. Ghirlanda, F. Govoni, A. Ingallinera, M. Johnston-Hollitt, M. Markevitch, A. Mesinger, V. Moss, F. Nicastro, P. Padovani, F. Panessa, L. Piro, G. Ponti, G. Pratt, E. M. Rossi, E. Sadler, M. Sasaki, R. Soria, I. Stevens, R. van Weeren, F. Vazza, N. Webb
Submitted Tuesday 24 July 2018 @ 13:07:48 GMT
79 pages, 28 figures. A high resolution version of the White Paper is available here: https://drive.google​.com/open?id=1HpuGUl​DGl2oWHV7j7fQPDYnkZZ​15af2I

The Advanced Telescope for High Energy Astrophysics (Athena) is the X-ray observatory large mission selected by the European Space Agency (ESA), within its Cosmic Vision 2015-2025 programme, to address the "Hot and Energetic Universe" scientific theme (Nandra et al. 2013), and it is provisionally due for launch in the early 2030s. The Square Kilometer Array (SKA) is the next generation radio observatory and consists of two telescopes, one comprised of dishes operating at mid frequencies (SKA1-MID) and located in South Africa, and the other comprised of Log-Periodic antennas operating at low radio frequencies (SKA1-LOW), which will be located in Australia (Braun et al. 2017). The scientific commissioning of the radio telescope is planned to begin in 2021-2022. The SKA-Athena Synergy Team (SAST) has been tasked to single out the potential scientific synergies between Athena and SKA. The astrophysical community was involved in this exercise primarily through a dedicated SKA-Athena Synergy Workshop, which took place on April 24-25, 2017 at SKAO, Jodrell Bank, Manchester. The final result of the synergy exercise, this White Paper, describes in detail a number of scientific opportunities that will be opened up by the combination of Athena and SKA, these include: 1. the Cosmic Dawn; 2. the Evolution of black holes and galaxies; 3. Active galaxy feedback in galaxy clusters; 4. Non-thermal phenomena in galaxy clusters; 5. Detecting the cosmic web; 6. Black-hole accretion physics and astrophysical transients; 7. Galactic astronomy: stars, planets, pulsars and supernovae.

[77] arXiv:1807.09073v1 [pdf, vox]

The flux distribution of individual blazars as a key to understand the dynamics of particle acceleration

Atreyee Sinha, Rukaiya Khatoon, Ranjeev Misra, Sunder Sahayanathan, Soma Mandal, Rupjyoti Gogoi, Nilay Bhatt
Submitted Tuesday 24 July 2018 @ 12:49:52 GMT
Accepted for publication in MNRAS Letters, 5 pages, 5 figures

The observed log-normal flux distributions in the high energy emission from blazars have been interpreted as being due to variability stemming from non-linear multiplicative processes generated dynamically from the accretion disc. On the other hand, rapid minute scale variations in the flux point to a compact emitting region inside the jet, probably disconnected from the disc. In this work, we show that linear Gaussian variations of the intrinsic particle acceleration or escape time-scales can produce distinct non-Gaussian flux distributions, including log-normal ones. Moreover, the spectral index distributions can provide confirming evidence for the origin of the variability. Thus, modelling of the flux and index distributions can lead to quantitative identification of the micro-physical origin of the variability in these sources. As an example, we model the X-ray flux and index distribution of Mkn 421 obtained from over 9 years of MAXI observations and show that the variability in the X-ray emission is driven by Gaussian fluctuations of the particle acceleration process rather than that of the escape rate.

[78] arXiv:1807.09071v1 [pdf, vox]

Pulse profiles of highly compact pulsars in general relativity

Hajime Sotani, Umpei Miyamoto
Submitted Tuesday 24 July 2018 @ 12:44:32 GMT
accepted for publication in PRD

Gravitational light bending by compact stars is an important astrophysical phenomenon. The bending angle depends on the stellar compactness, which is the ratio of stellar mass $M$ to radius $R$. In this paper, we investigate the pulse profile of highly compact rotating neutron stars for which the bending angle exceeds $\pi/2$. When $M/R > 0.284$ (the bending angle becomes equal to $\pi/2$ for the stellar model with $M/R=0.284$), such a large bending happens, resulting in that a photon emitted from any position on the stellar surface can reach an observer. First, we classify the parameter plane of inclination angle $i$ and angle $\Theta$ between the rotation axis and the normal on the hot spot by the number of photon paths reaching the observer. Then, we estimate the time-dependent flux of photons emitted from two hot spots on the rotating neutron star, associated with the magnetic polar caps, for various combinations of $i$ and $\Theta$, and for two values of compactness, assuming that the stellar rotation is not so fast that the frame dragging and the stellar deformation are negligible. As the result, we find that the pulse profiles of highly compact neutron stars are qualitatively different from those for the standard neutron stars. In particular, the ratio of the maximum observed flux to the minimum one is significantly larger than that for the standard neutron stars. This study suggests that one would be able to constrain the equation of state for neutron stars through the observation of pulse profile with angles $i$ and $\Theta$ determined by other methods.

[79] arXiv:1807.09057v1 [pdf, vox]

Failure of the stochastic approach to inflation in constant-roll and ultra-slow-roll

Diego Cruces, Cristiano Germani, Tomislav Prokopec
Submitted Tuesday 24 July 2018 @ 12:05:31 GMT
16 pages

After giving a pedagogical review we clarify that the stochastic approach to inflation is generically valid only at zeroth order in the (geometrical) slow-roll parameter $\epsilon_1$ if and only if $\epsilon_1\ll 6/\epsilon_2^2$, with the notable exception of slow-roll. This is due to the failure of the separate universe approach. As a byproduct, by keeping the formalism in its regime of validity, we show that quantum diffusion in ultra-slow-roll might only contribute to the power spectrum at sub-leading orders in slow-roll, and thus, it is irrelevant.

[80] arXiv:1807.09024v1 [pdf, vox]

Deep learning techniques applied to the physics of extensive air showers

A. Guillen, A. Bueno, J. M. Carceller, J. C. Martinez-Velazquez, G. Rubio, C. J. Todero Peixoto, P. Sanchez-Lucas
Submitted Tuesday 24 July 2018 @ 10:39:46 GMT
21 pages, 16 figures. Version submitted to the Journal of Computational Physics

Deep neural networks are a powerful technique that have found ample applications in several branches of Physics. In this work, we apply machine learning algorithms to a specific problem of Cosmic Ray Physics: the estimation of the muon content of extensive air showers when measured at the ground. As a working case, we explore the performance of a deep neural network applied to the signals recorded by the water-Cherenkov detectors of the Surface Detector Array of the Pierre Auger Observatory. We apply deep learning architectures to large sets of simulated data. The inner structure of the neural network is optimized through the use of genetic algorithms. To obtain a prediction of the recorded muon signal in each individual detector, we train neural networks with a mixed sample of light, intermediate and heavy nuclei. When true and predicted signals are compared at detector level, the primary values of the Pearson correlation coefficients are above 95\%. The relative errors of the predicted muon signals are below 10\% and do not depend on the event energy, zenith angle, total signal size, distance range or the hadronic model used to generate the events.

[81] arXiv:1807.09021v1 [pdf, vox]

Crust-magnetosphere coupling during magnetar evolution and implications for the surface temperature

Taner Akgün, Pablo Cerdá-Durán, Juan Antonio Miralles, José A. Pons
Submitted Tuesday 24 July 2018 @ 10:34:10 GMT
9 pages, 9 figures

We study the coupling of the force-free magnetosphere to the long-term internal evolution of a magnetar. We allow the relation between the poloidal and toroidal stream functions - that characterizes the magnetosphere - to evolve freely without constraining its particular form. We find that, on timescales of the order of kyrs, the energy stored in the magnetosphere gradually increases, as the toroidal region grows and the field lines expand outwards. This continues until a critical point is reached beyond which force-free solutions for the magnetosphere can no longer be constructed, likely leading to some large scale magnetospheric reorganization. The energy budget available for such events can be as high as several $10^{45}\,$erg for fields of $10^{14}\,$G. Subsequently, starting from the new initial conditions, the evolution proceeds in a similar manner. The timescale to reach the critical point scales inversely with the magnetic field amplitude. Allowing currents to pass through the last few meters below the surface, where the magnetic diffusivity is orders of magnitude larger than in the crust, should give rise to a considerable amount of energy deposition through Joule heating. We estimate that, the effective surface temperature could increase locally from $\sim 0.1\,$keV to $\sim 0.3 - 0.6\,$keV, in good agreement with observations. Similarly, the power input from the interior into the magnetosphere could be as high as $10^{35} - 10^{36}\,$erg/s, which is consistent with peak luminosities observed during magnetar outbursts. Therefore, a detailed treatment of currents flowing through the envelope may be needed to explain the thermal properties of magnetars.

[82] arXiv:1807.09004v1 [pdf, vox]

A Dark Matter Hurricane: Measuring the S1 Stream with Dark Matter Detectors

Ciaran A. J. O'Hare, Christopher McCabe, N. Wyn Evans, GyuChul Myeong, Vasily Belokurov
Submitted Tuesday 24 July 2018 @ 10:06:46 GMT
21 pages, 11 figures. To be submitted to PRD

The recently discovered S1 stream passes through the Solar neighbourhood on a low inclination, counter-rotating orbit. The progenitor of S1 is a dwarf galaxy with a total mass comparable to the present-day Fornax dwarf spheroidal, so the stream is expected to have a significant DM component. We compute the effects of the S1 stream on WIMP and axion detectors as a function of the density of its unmeasured dark component. In WIMP detectors the S1 stream supplies more high energy nuclear recoils so will marginally improve DM detection prospects. We find that even if S1 comprises less than 10% of the local density, multi-ton xenon WIMP detectors can distinguish the S1 stream from the bulk halo in the relatively narrow mass range between 5 and 25 GeV. In directional WIMP detectors such as CYGNUS, S1 increases DM detection prospects more substantially since it enhances the anisotropy of the WIMP signal. Finally, we show that axion haloscopes possess by far the greatest potential sensitivity to the S1 stream. Once the axion mass has been discovered, the distinctive velocity distribution of S1 can easily be extracted from the axion power spectrum.

[83] arXiv:1807.09001v1 [pdf, vox]

On the orbital properties of millisecond pulsar binaries

C. Y. Hui, Kinwah Wu, Qin Han, A. K. H. Kong, P. H. T. Tam
Submitted Tuesday 24 July 2018 @ 09:57:29 GMT
13 pages, 4 figures, 2 tables, accepted for publication in ApJ

We report a detailed analysis of the orbital properties of binary millisecond pulsar (MSP) with a white dwarf (WD) companion. Positive correlations between the orbital period $P_{\rm b}$ and eccentricity $\epsilon$ are found in two classes of MSP binaries with a He WD and with a CO/ONeMg WD, though their trends are different. The distribution of $P_{\rm b}$ is not uniform. Deficiency of sources at $P_{\rm b}\sim35-50$~days (Gap 1) have been mentioned in previous studies. On the other hand, another gap at $P_{\rm b}\sim2.5-4.5$~days (Gap 2) is identified for the first time. Inspection of the relation between $P_{\rm b}$ and the companion masses $M_{\rm c}$ revealed the subpopulations of MSP binaries with a He WD separated by Gap 1, above which $P_{\rm b}$ is independent of $M_{\rm c}$ (horizontal branch) but below which $P_{\rm b}$ correlates strongly with $M_{\rm c}$ (lower branch). Distinctive horizontal branch and lower branch separated by Gap 2 were identified for the MSP binaries with a CO/ONeMg WD at shorter $P_{\rm b}$ and higher $M_{\rm c}$. Generally, $M_{\rm c}$ are higher in the horizontal branch than in the lower branch for the MSP binaries with a He WD. These properties can be explained in terms of a binary orbital evolution scenario in which the WD companion was ablated by a pulsar wind in the post mass-transfer phase.

[84] arXiv:1807.08975v1 [pdf, vox]

Higher dispersion and efficiency Bragg gratings for optical spectroscopy

Will Saunders, Kai Zhang, Thomas Flügel-Paul
Submitted Tuesday 24 July 2018 @ 09:09:36 GMT
10 pages. SPIE 10706-187

Massively multiplexed spectroscopic stellar surveys such as MSE present enormous challenges in the spectrograph design. The combination of high multiplex, large telescope aperture, high resolution (R~40,000) and natural seeing implies that multiple spectrographs with large beam sizes, large grating angles, and fast camera speeds are required, with high cost and risk. An attractive option to reduce the beam size is to use Bragg-type gratings at much higher angles than hitherto considered. As well as reducing the spectrograph size and cost, this also allows the possibility of very high efficiency due to a close match of s and p-polarization Bragg efficiency peaks. The grating itself could be a VPH grating, but Surface Relief (SR) gratings offer an increasingly attractive alternative, with higher maximum line density and better bandwidth. In either case, the grating needs to be immersed within large prisms to get the light to and from the grating at the required angles. We present grating designs and nominal spectrograph designs showing the efficiency gains and size reductions such gratings might allow for the MSE high resolution spectrograph.

[85] arXiv:1807.08972v1 [pdf, vox]

Copper abundance from Cu I and Cu II lines in metal-poor star spectra: NLTE vs LTE

S. A. Korotin, S. M. Andrievsky, A. V. Zhukova
Submitted Tuesday 24 July 2018 @ 09:03:12 GMT
6 pages, 4 figures

We checked consistency between the copper abundance derived in six metal-poor stars using UV Cu II lines (which are assumed to form in LTE) and UV Cu I lines (treated in NLTE). Our program stars cover the atmosphere parameters which are typical for intermediate temperature dwarfs (effective temperature is in the range from approximately 5800 to 6100 K, surface garvity is from 3.6 to 4.5, metallicity is from about -1 to -2.6 dex). We obtained a good agreement between abundance from these two sets of the lines, and this testifies about reliability of our NLTE copper atomic model. We confirmed that no underabundace of this element is seen at low metallicities (the mean [Cu/Fe] value is about -0.2 dex, while as it follows from the previous LTE studies copper behaves as a secondary element and [Cu/Fe] ratio in the range of [Fe/H from -2 to -3 dex should be about -1 dex). According to our NLTE data the copper behaves as a primary element at low metallicity regime. We also conclude that our new NLTE copper abundance in metal-poor stars requires significant reconsideration of this element yields in the explosive nucleosynthesis.

[86] arXiv:1807.08968v1 [pdf, vox]

Molecular filament formation and filament-cloud interaction: Hints from Nobeyama 45m telescope observations

Doris Arzoumanian, Yoshito Shimajiri, Shu-ichiro Inutsuka, Tsuyoshi Inoue, Kengo Tachihara
Submitted Tuesday 24 July 2018 @ 09:01:03 GMT
Accepted for publication in PASJ (Publications of the Astronomical Society of Japan)

We present Nobeyama 45m telescope C18O, 13CO, and 12CO(1-0) mapping observations towards an interstellar filament in the Taurus molecular cloud. We investigate the gas velocity structure along the filament and in its surrounding parent cloud. The filament is detected in the optically thin C18O emission as a single velocity component, ~1pc long, ~0.06pc wide structure. The C18O emission traces dust column densities larger than ~5x10^21 cm-2. The line-of-sight (LOS) velocity fluctuates along the filament crest with an average amplitude of ~0.2 km/s. The 13CO and 12CO integrated intensity maps show spatially extended emission around the elongated filament. We identify three extended structures with LOS velocities redshifted and blueshifted with respect to the average velocity of the filament identified in C18O. Based on combined analyses of velocity integrated channel maps and intensity variations of the optically thick 12CO spectra on and off the filament, we propose a 3-dimensional structure of the cloud surrounding the filament. We further suggest a multi-interaction scenario where sheet-like extended structures interact, in space and time, with the filament and are responsible for its compression and/or disruption, playing an important role in the star formation history of the filament. We also identify, towards the same field, a very faint filament showing a velocity field compatible with the filament formation process proposed by Inoue et al. (2017), where a filament is formed due to convergence of a flow of matter generated by the bending of the ambient magnetic field structure induced by an interstellar shock compression.

[87] arXiv:1807.08574v2 [pdf, vox]

XMM-Newton detection of the 2.1 ms coherent pulsations from IGR J17379-3747

A. Sanna, E. Bozzo, A. Papitto, A. Riggio, C. Ferrigno, T. Di Salvo, R. Iaria, S. M. Mazzola, N. D'Amico, L. Burderi
Submitted Tuesday 24 July 2018 @ 08:43:55 GMT
5 pages, 2 figures, 1 table. Accepted for publication in A&A

We report on the detection of X-ray pulsations at 2.1 ms from the known X-ray burster IGR J17379-3747 using XMM-Newton. The coherent signal shows a clear Doppler modulation from which we estimate an orbital period of ~1.9 hours and a projected semi-major axis of ~8 lt-ms. Taking into account the lack of eclipses (inclination angle of < 75 deg) and assuming a neutron star mass of 1.4 Msun, we estimated a minimum companion star of ~0.06 Msun. Considerations on the probability distribution of the binary inclination angle make less likely the hypothesis of a main-sequence companion star. On the other hand, the close correspondence with the orbital parameters of the accreting millisecond pulsar SAX J1808.4-3658 suggests the presence of a bloated brown dwarf. The energy spectrum of the source is well described by a soft disk black-body component (kT ~0.45 keV) plus a Comptonisation spectrum with photon index ~1.9. No sign of emission lines or reflection components is significantly detected. Finally, combining the source ephemerides estimated from the observed outbursts, we obtained a first constraint on the long-term orbital evolution of the order of dP_orb/dt = (-2.5 +/- 2.3)E-12 s/s.

[88] arXiv:1807.08953v1 [pdf, vox]

The interacting late-type host galaxy of the radio-loud narrow-line Seyfert 1 IRAS 20181-2244

M. Berton, E. Congiu, S. Ciroi, S. Komossa, M. Frezzato, F. Di Mille, S. Antón, R. Antonucci, A. Caccianiga, P. Coppi, E. Järvelä, J. Kotilainen, A. Lähteenmäki, S. Mathur, S. Chen, V. Cracco, G. La Mura, P. Rafanelli
Submitted Tuesday 24 July 2018 @ 08:26:36 GMT
7 pages, 5 figures, 1 table, submitted to ApJ

Narrow-line Seyfert 1 galaxies (NLS1s) are a class of active galactic nuclei (AGN). Their physical properties can be either interpreted in terms of evolution, suggesting that they are a young phase of AGN life, or inclination, under the hypothesis of a disk-like broad-line region observed pole-on. To distinguish between these two hypotheses, host galaxy morphology is a very helpful tool because it can provide an independent estimate of the black hole mass. In this work we present the results of a morphological analysis of the host galaxy of the radio-loud NLS1 IRAS 20181-2244 observed with the 6.5m Baade Telescope of the Las Campanas Observatory. The GALFIT analysis ran on the Ks image, along with additional spectroscopic observations performed with the Nordic Optical Telescope, clearly revealed the presence of an interacting system of two disk galaxies. The presence of a disk hosting this NLS1 is supportive of the evolutionary hypothesis. This analysis, along with other results presented in the literature, might suggest that two subclasses of radio-loud NLS1 exist. One represents the young evolutionary phase of AGN life, and the other is observed pole-on. Further morphological studies are needed to discern between the two groups.

[89] arXiv:1807.08932v1 [pdf, vox]

Laser and Radio Tracking for Planetary Science Missions - A Comparison

Dominic Dirkx, Ivan Prochazka, Sven Bauer, Pieter Visser, Ron Noomen, Leonid I. Gurvits, Bert Vermeersen
Submitted Tuesday 24 July 2018 @ 07:30:04 GMT
Accepted for publication in Journal of Geodesy

At present, tracking data for planetary missions largely consists of radio observables: range-rate range and angular position. Future planetary missions may use Interplanetary Laser Ranging (ILR) as a tracking observable. Two-way ILR will provide range data that are about 2 orders of magnitude more accurate than radio-based range data. ILR does not produce Doppler data, however. In this article, we compare the relative strength of radio Doppler and laser range data for the retrieval of parameters of interest in planetary missions, to clarify and quantify the science case of ILR, with a focus on geodetic observables. We first provide an overview of the near-term attainable quality of ILR, in terms of both the realization of the observable and the models used to process the measurements. Subsequently, we analyze the sensitivity of radio-Doppler and laser-range measurements in representative mission scenarios. We use both an analytical approximation and numerical analyses of the relative sensitivity of ILR and radio Doppler observables for more general cases. We show that mm-precise range normal points are feasible for ILR, but mm-level accuracy and stability is unlikely to be attained, due to a combination of instrumental and model errors. ILR has the potential for superior performance in observing signatures in the data with a characteristic period of greater than 0.33-1.65 hours This indicates that Doppler tracking will typically remain the method of choice for gravity field determination and spacecraft orbit determination in planetary missions. Laser ranging data, however, are shown to have a significant advantage for the retrieval of rotational and tidal characteristics from landers. Similarly, laser ranging data will be superior for the construction of planetary ephemerides and the improvement of solar system tests of gravitation.

[90] arXiv:1807.08923v1 [pdf, vox]

Late Engine Activity of GRB 161017A Revealed by Early Optical Observations

Yutaro Tachibana, Makoto Arimoto, Katsuaki Asano, Shohei Harita, Taichi Fujiwara, Taketoshi Yoshii, Ryosuke Itoh, Katsuhiro L. Murata, Yoichi Yatsu, Kotaro Morita, Nobuyuki Kawai
Submitted Tuesday 24 July 2018 @ 06:22:42 GMT

The long gamma-ray burst GRB 161017A was detected by Fermi and Swift, and its afterglow was observed by the MITSuME 50-cm optical telescope promptly about 50 s after the burst. Early optical observations revealed that the optical lightcurve exhibits a plateau and rebrightening in the early afterglow phase about 500 and 5000 s after the trigger, respectively. By investigating the behavior of the spectral and temporal flux variation, it was found that the plateau and re-brightening cannot be explained in the context of the simple standard afterglow model. These observational features can be explained with two independent refreshed shocks, which indicate the long-acting central engine. We evaluated the physical parameters of the subsequent shells, and we then determined the kinetic energy ratio of the two colliding shells to the leading shell to be roughly 1 and 8, respectively. In addition, two prominent X-ray flares about 200 s after the trigger may be signatures of delayed ejections of the energetic jets responsible for the refreshed shocks. Such late activity of the central engine and X-ray flares play a crucial role in understanding the mechanisms for jet formation and photon emission.

[91] arXiv:1807.08895v1 [pdf, vox]

The Atacama Cosmology Telescope: CO(J = 3 - 2) mapping and lens modeling of an ACT-selected dusty star-forming galaxy

J. Rivera, A. J. Baker, P. A. Gallardo, M. Gralla, A. I. Harris, K. M. Huffenberger, J. P. Hughes, C. R. Keeton, C. H. Lopez-Caraballo, T. A. Marriage, B. Partridge, J. Sievers, A. S. Tagore, F. Walter, A. Weiss, E. J. Wollack
Submitted Tuesday 24 July 2018 @ 03:45:07 GMT
7 pages, 5 figures, submitted to ApJ

We report Northern Extended Millimeter Array (NOEMA) CO($J = 3 - 2$) observations of the dusty star-forming galaxy ACT-S J0209941+001557 at $z = 2.5528$, which was detected as an unresolved source in the Atacama Cosmology Telescope (ACT) equatorial survey. Our spatially resolved spectral line data support the derivation of a gravitational lens model from 37 independent velocity channel maps using a pixel-based algorithm, from which we infer a velocity-dependent magnification factor $\mu \approx 4-27$ with a luminosity-weighted mean $\left<\mu\right>\ap​prox 14$. The resulting source-plane reconstruction is consistent with a rotating disk, although other scenarios cannot be ruled out by our data. After correction for lensing, we derive a line luminosity $L^{\prime}_{\rm CO(3-2)}= (5.06\pm 0.12) \times 10^{10}\,{\rm \,K\,km\,s^{-1}\,pc^​{2}}$, a cold gas mass $M_{{\rm gas}}= (3.52 \pm 0.21) \times 10^{10}\,M_{\odot}$, a dynamical mass $M_{\rm dyn}\,{\rm sin}^2\,i = 4.0^{+1.7}_{-1.3} \times 10^{10}\,M_{\odot}$, and a gas mass fraction $f_{\rm gas}\,{\rm csc}^2\,i = 0.9^{+0.5}_{-0.3}$. The line brightness temperature ratio of $r_{3,1}\approx 1.6$ relative to a Green Bank Telescope CO($J=1-0$) detection may be elevated by a combination of external heating of molecular clouds, differential lensing, and/or pointing errors.

[92] arXiv:1807.08892v1 [pdf, vox]

On ANITA's sensitivity to long-lived, charged massive particles

Amy Connolly, Patrick Allison, Oindree Banerjee
Submitted Tuesday 24 July 2018 @ 03:20:42 GMT
5 pages, 5 figures, to be submitted to Astropart. Phys. J

We propose that the Antarctic Impulsive Transient Antenna (ANITA) can serve as a detector for long-lived, charged particles, through its measurement of extensive air showers from secondary leptons. To test this on an example model, we simulate the production of staus inside the earth from interactions between ultra-high energy neutrinos and nuclei. We propose that results of ANITA searches for upgoing air showers can be interpreted in terms of constraints on long-lived, charged massive particles (CHAMPs) and consider a supersymmetric partner of the tau lepton, the stau, as an example of such a particle. Exploring the parameter space in stau mass and lifetimes, we find that the stau properties that lead to an observable signal in ANITA are highly energy dependent. At $10^{18.5}$ eV, we find that the best constraints on the product of the neutrino flux and the stau production cross section would be placed near $m_{\tilde{\tau}}=$1 TeV and $\tau_{\tilde{\tau}}​=$10 ns. Thus ANITA could be sensitive to new physics in a region of parameter space that is unconstrained by experiments at the Large Hadron Collider.

[93] arXiv:1807.08890v1 [pdf, vox]

Modeled Temperature-Dependen​t Clouds with Radiative Feedback in Hot Jupiter Atmospheres

Michael Roman, Emily Rauscher
Submitted Tuesday 24 July 2018 @ 03:07:21 GMT
20 pages, 11 figures, submitted to AAS Journals

Using a general circulation model with newly implemented cloud modeling, we investigate how radiative feedback can self-consistently shape condensate cloud distributions, temperatures, and fluxes in a hot Jupiter atmosphere. We apply a physically motivated but simple parameterization of condensate clouds in which the temperature determines the cloud distribution, and we evaluate how different assumptions of vertical mixing and aerosol scattering parameters affect predictions. We compare results from cases in which the aerosols are simply included in the last step of the simulation (i.e. post-processed) to cases in which clouds and their radiative feedback are actively included throughout the duration of the simulation. When clouds and radiative feedback were actively included, cloud cover decreased at equatorial regions and increased towards the poles relative to the post-processed solutions. The resulting phase curves also differed between the two approaches; the post-processed cloud simulations predicted weaker day-night contrasts in emission and greater eastward shifts in the maximum emission compared to the active cloud modeling. This illustrates the importance of cloud radiative feedback and shows that post-processing will provide inaccurate solutions when clouds are thick enough to provide significant scattering.

[94] arXiv:1807.08879v1 [pdf, vox]

Relative Likelihood of Success in the Searches for Primitive versus Intelligent Extraterrestrial Life

Manasvi Lingam, Abraham Loeb
Submitted Tuesday 24 July 2018 @ 01:57:12 GMT
19 pages; 0 figures

We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Our analysis suggests that the search for technosignatures may potentially merit a minimum funding level of $\$1$ million per year.

[95] arXiv:1807.08872v1 [pdf, vox]

SDSS-IV MaNGA: The intrinsic shape of slow rotator early-type galaxies

Hongyu Li, Shude Mao, Michele Cappellari, Mark T. Graham, Eric Emsellem, R. J. Long
Submitted Tuesday 24 July 2018 @ 01:08:33 GMT
Accepted for publication in ApJL, 10 pages, 4 figures, 1 table

By inverting the distributions of galaxies' apparent ellipticities and misalignment angles (measured around the projected half-light radius $R_{\rm e}$) between their photometric and kinematic axes, we study the intrinsic shape distribution of 189 slow rotator early-type galaxies with stellar masses $2\times 10^{11} M_{\odot}<M_\ast<2\t​imes 10^{12} M_{\odot}$, extracted from a sample of about 2200 galaxies with integral-field stellar kinematics from the DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow rotators, Graham+18 showed that there is clear structure in the misalignment angle distribution, with two peaks at both $0^{\circ}$ and $90^{\circ}$ misalignment (characteristic of oblate and prolate rotation respectively). Here we invert the observed distribution from Graham+18. The large sample allows us to go beyond the known fact that slow rotators are weakly triaxial and to place useful constraints on their intrinsic triaxiality distribution (around $1R_{\rm e}$) for the first time. The shape inversion is generally non-unique. However, we find that, for a wide set of model assumptions, the observed distribution clearly requires a dominant triaxial-oblate population. For some of our models, the data suggest a hint for a minor triaxial-prolate population, but a dominant prolate population is ruled out.

[96] arXiv:1807.08867v1 [pdf, vox]

Wobbling galaxy spin axes in dense environments

Jaehyun Lee, Suk Kim, Hyunjin Jeong, Rory Smith, Hoseung Choi, Ho Seong Hwang, Seok-Joo Joo, Hak-Sub Kim, Yongdae Lee, Sukyoung K. Yi
Submitted Tuesday 24 July 2018 @ 00:59:50 GMT
17 pages, 10 figures, Accepted for publication in ApJ

The orientation of galaxy spin vectors within the large scale structure has been considered an important test of our understanding of structure formation. We investigate the angular changes of galaxy spin vectors in clusters - denser environments than are normally focused upon, using hydrodynamic zoomed simulations of 17 clusters YZiCS and a set of complementary controlled simulations. The magnitude by which galaxies change their spin vector is found to be a function of their rotational support with larger cumulative angular changes of spin vectors when they have initially lower $V_{\theta}/\sigma$. We find that both mergers and tidal perturbations can significantly swing spin vectors, with larger changes in spin vector for smaller pericentre distances. Strong tidal perturbations are also correlated with the changes in stellar mass and specific angular momentum of satellite galaxies. However, changes in spin vector can often result in a canceling out of previous changes. As a result, the integrated angular change is always much larger than the angular change measured at any instant. Also, overall the majority of satellite galaxies do not undergo mergers or sufficiently strong tidal perturbation after infall into clusters, and thus they end up suffering little change to their spin vectors. Taken as a whole, these results suggest that any signatures of spin alignment from the large scale structure will be preserved in the cluster environment for many gigayears.

[97] arXiv:1807.08864v1 [pdf, vox]

Observing Black Hole Binaries in nearby Globular Clusters with LISA: Source Depletion from General Relativistic Dynamics

Johan Samsing, Daniel J. D'Orazio
Submitted Tuesday 24 July 2018 @ 00:43:13 GMT
8 pages. 1 figure. comments welcome

We derive the observable gravitational wave (GW) peak frequency ($f$) distribution of binary black holes (BBHs) that currently reside inside their globular clusters (GCs), with and without General Relativity (GR) effects included in the dynamical evolution of the BBHs. Recent Newtonian studies have reported that a notable number of nearby non-merging BBHs, i.e. those BBHs that are expected to undergo further dynamical interactions before merger, in GCs are likely to be observable by LISA. However, our GR calculations show that the distribution of $\log f$ for the non-merging BBH population above $\sim 10^{-3.5}$ Hz scales as $f^{-34/9}$ instead of the $f^{-2/3}$ scaling found in the Newtonian case. This leads to an approximately two-orders-of-magnit​ude reduction in the expected number of GW sources at $\sim 10^{-3}$ Hz, which lead us to conclude that observing nearby BBHs with LISA is not as likely as has been claimed in the recent literature. In fact, our results suggest that it might be more likely that LISA detects the population of BBHs that will merge before undergoing further interactions. This interestingly suggests that the BBH merger rate derived from LIGO can be used to forecast the number of nearby LISA sources, as well as providing insight into the fraction of BBH mergers forming in GCs.

Submitted Mon, 23 Jul 2018

[98] arXiv:1807.08860v1 [pdf, vox]

Evolution of the cold gas fraction and the star formation history: Prospects with current and future radio facilities

S. J. Curran
Submitted Monday 23 July 2018 @ 23:42:41 GMT
Accepted for publication in PASA

It has recently been shown that the abundance of cold neutral gas may follow a similar evolution as the star formation history. This is physically motivated, since stars form out of this component of the neutral gas and if the case, would resolve the longstanding issue that there is a clear disparity between the total abundance of neutral gas and star forming activity over the history of the Universe. Radio-band 21-cm absorption traces the cold gas and comparison with the Lyman-alpha absorption, which traces all of the gas, provides a measure of the cold gas fraction or the spin temperature. The recent study has shown that the spin temperature (degenerate with the ratio of the absorber/emitter extent) appears to be anti-correlated with the star formation density, undergoing a similar steep evolution as the star formation rate over redshifts of 0 < z < 3, whereas the total neutral hydrogen exhibits little evolution. Above z > 3, where the SFR shows a steep decline with redshift, there is insufficient 21-cm data to determine whether the spin temperature continues to follow the SFR. Knowing this is paramount in ascertaining whether the cold neutral gas does trace the star formation over the Universe's history. We explore the feasibility of resolving this with 21-cm observations of the largest contemporary sample of reliable damped Lyman-alpha absorption systems and conclude that, while today's largest radio interferometers can reach the required sensitivity at z < 3.5, the Square Kilometre Array is required to probe to higher redshifts.

[99] arXiv:1807.08847v1 [pdf, vox]

Parametric Study of the Rossby Wave Instability in a Two-dimensional Barotropic Disk II: Non-Linear Calculations

Tomohiro Ono, Takayuki Muto, Kengo Tomida, Zhaohuan Zhu
Submitted Monday 23 July 2018 @ 22:11:22 GMT
32 pages, 19 figures, 4 Tables, accepted for publication in ApJ

Vortices in protoplanetary disks have attracted attention since the discovery of lopsided structures. One of the possible mechanisms for producing vortices is the Rossby Wave Instability (RWI). In our previous work, we have performed detailed linear stability analyses of the RWI with various initial conditions. In this paper, we perform numerical simulations of the vortex formation by the RWI in 2D barotropic disks using the Athena++ code. As initial conditions, we consider axisymmetric disks with a Gaussian surface density bump of various contrasts and half-widths. Perturbations grow as expected from the linear stability analyses in the linear and weakly non-linear regimes. After the saturation, multiple vortices are formed in accordance with the most unstable azimuthal mode and coalesce one after another. In the end, only one quasi-stationary vortex (the RWI vortex) remains, which migrates inward. During the RWI evolution, the axisymmetric component approaches the stable configuration. We find that the axisymmetric component reaches the marginally stable state for the most unstable azimuthal mode at the saturation and the marginally stable state for the m = 1 mode at the final vortex merger. We investigate the structure and evolution of the RWI vortices. We obtain some empirical relations between the properties of the RWI vortices and the initial conditions. Using tracer particle analyses, we find that the RWI vortex can be considered as a physical entity like a large fluid particle. Our results provide a solid theoretical ground for quantitative interpretation of the observed lopsided structures in protoplanetary disks.

[100] arXiv:1807.08845v1 [pdf, vox]

SOFIA/FORCAST Observations of the Luminous Blue Variable Candidates MN 90 and HD 168625

Ryan Arneson, Dinesh Shenoy, Nathan Smith, Robert Gehrz
Submitted Monday 23 July 2018 @ 21:59:01 GMT
17 pages, 5 figures, accepted for publication in ApJ

We present SOFIA/FORCAST imaging of the circumstellar dust shells surrounding the luminous blue variable (LBV) candidates MN 90 and HD 168625 to quantify the mineral abundances of the dust and to constrain the evolutionary state of these objects. Our image at 37.1 micron of MN 90 shows a limb-brightened, spherical dust shell. A least-squares fit to the spectral energy distribution of MN 90 yields a dust temperature of 59 \pm 10 K, with the peak of the emission at 42.7 micron. Using 2-Dust radiative transfer code, we estimate for MN 90 that mass-loss occurred at a rate of (7.3 \pm 0.4)x10^-7 M_sun/yr x (v_exp/50 km/s) to create a dust shell with a dust mass of (3.2 \pm 0.1)x10^-2 M_sun. Our images between 7.7 - 37.1 micron of HD 168625 complement previously obtained mid-IR imaging of its bipolar nebulae. The SOFIA/FORCAST imaging of HD 168625 shows evidence for the limb-brightened peaks of an equatorial torus. We estimate a dust temperature of 170 \pm 40 K for the equatorial dust surrounding HD 168625, with the peak of the emission at 18.3 micron. Our 2-Dust model for HD 168625 estimates that mass-loss occurred at a rate of (3.2 \pm 0.2)x10^-7 M_sun/yr to create a dust torus/shell with a dust mass of (2.5 \pm 0.1)x10^-3 M_sun.

[101] arXiv:1807.08840v1 [pdf, vox]

Ergoregion instability of exotic compact objects: electromagnetic and gravitational perturbations and the role of absorption

Elisa Maggio, Vitor Cardoso, Sam R. Dolan, Paolo Pani
Submitted Monday 23 July 2018 @ 21:42:58 GMT
11 pages, 4 figures

Spinning horizonless compact objects may be unstable against an 'ergoregion instability'. We investigate this mechanism for electromagnetic perturbations of ultracompact Kerr-like objects with a reflecting surface, extending previous (numerical and analytical) work limited to the scalar case. We derive an analytical result for the frequency and the instability time scale of unstable modes which is valid at small frequencies. We argue that our analysis can be directly extended to gravitational perturbations of exotic compact objects in the black-hole limit. The instability for electromagnetic and gravitational perturbations is generically stronger than in the scalar case and it requires larger absorption to be quenched. We argue that exotic compact objects with spin $\chi\lesssim 0.7$ ($\chi\lesssim 0.9$) should have an absorption coefficient of at least $0.3\%$ ($6\%$) to remain linearly stable, and that an absorption coefficient of at least $\approx60\%$ would quench the instability for any spin. We also show that - in the static limit - the scalar, electromagnetic, and gravitatonal perturbations of the Kerr metric are related to one another through Darboux transformations.

[102] arXiv:1807.08832v1 [pdf, vox]

Ground Layer Adaptive Optics for the W. M. Keck Observatory: Feasibility Study

J. R. Lu, M. Chun, S. M. Ammons, K. Bundy, R. Dekany, T. Do, D. Gavel, M. Kassis, O. Lai, C. L. Martin, C. Max, C. Steidel, L. Wang, K. Westfall, P. Wizinowich
Submitted Monday 23 July 2018 @ 21:13:57 GMT
2018 Proceedings of the SPIE; published

Ground-layer adaptive optics (GLAO) systems offer the possibility of improving the "seeing" of large ground-based telescopes and increasing the efficiency and sensitivity of observations over a wide field-of-view. We explore the utility and feasibility of deploying a GLAO system at the W. M. Keck Observatory in order to feed existing and future multi-object spectrographs and wide-field imagers. We also briefly summarize science cases spanning exoplanets to high-redshift galaxy evolution that would benefit from a Keck GLAO system. Initial simulations indicate that a Keck GLAO system would deliver a 1.5x and 2x improvement in FWHM at optical (500 nm) and infrared (1.5 micron), respectively. The infrared instrument, MOSFIRE, is ideally suited for a Keck GLAO feed in that it has excellent image quality and is on the telescope's optical axis. However, it lacks an atmospheric dispersion compensator, which would limit the minimum usable slit size for long-exposure science cases. Similarly, while LRIS and DEIMOS may be able to accept a GLAO feed based on their internal image quality, they lack either an atmospheric dispersion compensator (DEIMOS) or flexure compensation (LRIS) to utilize narrower slits matched to the GLAO image quality. However, some science cases needing shorter exposures may still benefit from Keck GLAO and we will investigate the possibility of installing an ADC.

[103] arXiv:1807.08828v1 [pdf, vox]

SOXS: a wide band spectrograph to follow up transients

P. Schipani, S. Campana, R. Claudi, H. U. Käufl, M. Accardo, M. Aliverti, A. Baruffolo, S. Ben-Ami, F. Biondi, A. Brucalassi, G. Capasso, R. Cosentino, F. D'Alessio, P. D'Avanzo, O. Hershko, D. Gardiol, H. Kuncarayakti, M. Munari, A. Rubin, S. Scuderi, F. Vitali, J. Achrén, J. Antonio Araiza-Duran, I. Arcavi, A. Bianco, E. Cappellaro, M. Colapietro, M. Della Valle, O. Diner, S. D'Orsi, D. Fantinel, J. Fynbo, A. Gal-Yam, M. Genoni, M. Hirvonen, J. Kotilainen, T. Kumar, M. Landoni, J. Lehti, G. Li Causi, D. Loreggia, L. Marafatto, S. Mattila, G. Pariani, G. Pignata, M. Rappaport, D. Ricci, M. Riva, B. Salasnich, R. Zanmar Sanchez, S. Smartt, M. Turatto
Submitted Monday 23 July 2018 @ 21:01:27 GMT
12 pages, 14 figures, to be published in SPIE Proceedings 10702

SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ~ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase.

[104] arXiv:1807.08819v1 [pdf, vox]

The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor

Richard D'Souza, Eric F. Bell
Submitted Monday 23 July 2018 @ 20:38:27 GMT
Published in Nature Astronomy. Available here https://www.nature.c​om/articles/s41550-0​18-0533-x

Although the proximity of the Andromeda galaxy (M31) offers an opportunity to understand how mergers affect galaxies, uncertainty remains about M31's most important mergers. Previous studies focused individually on the giant stellar stream or the impact of M32 on M31's disk, thereby suggesting many substantial satellite interactions. Yet models of M31's disk heating and the similarity between the stellar populations of different tidal substructures in M31's outskirts both suggested a single large merger. M31's stellar halo (its outer low-surface-brightne​ss regions) is built up from the tidal debris of satellites and provides information about its important mergers. Here we use cosmological models of galaxy formation to show that M31's massive and metal-rich stellar halo, containing intermediate-age stars, dramatically narrows the range of allowed interactions, requiring a single dominant merger with a large galaxy (with stellar mass about 2.5 x 10^10 solar masses, the third largest member of the Local Group) about 2 Gyr ago. This single event explains many observations that were previously considered separately: M31's compact and metal-rich satellite M32 is likely to be the stripped core of the disrupted galaxy, its rotating inner stellar halo contains most of the merger debris, and the giant stellar stream is likely to have been thrown out during the merger. This interaction may explain M31's global burst of star formation about 2 Gyr ago in which approximately a fifth of its stars were formed. Moreover, M31's disk and bulge were already in place, suggesting that mergers of this magnitude need not dramatically affect galaxy structure.

[105] arXiv:1807.08818v1 [pdf, vox]

Alternative zebra-structure models in solar radio emission

G. P. Chernov
Submitted Monday 23 July 2018 @ 20:37:01 GMT
20 pages, 9 figures

In the literature, discussion continues about the nature of the zebra structure (ZS) in type IV radio bursts, and understanding even the most extended mechanism associated with double plasma resonance has been improved in series of works. Moreover, in the recent work (Ben\'a\v{c}hek, Karlick\'y, Yasnov, 2017) its ineffectiveness was shown under the usually adopted conditions in the radio source. In this case in a number of works we demonstrated the possibility of modeling with whistlers to explain many thin components of ZS stripes, taking into account the effects of scattering whistlers on fast particles. This situation stimulates the search for new mechanisms. For example, earlier we showed the importance of explosive instability, at least for large flares with the ejections of protons. In the system a weakly relativistic beam of protons, nonisothermic plasma, the slow beam mode of the space charge possesses negative energy, and in the triplet slow and fast beam modes and ion acoustic wave an explosive cascade of harmonics from ionic sound is excited. Electromagnetic waves in the form of ZS stripes appear as a result of the fast protons scattering on these harmonics. Such a mechanism can also be promising for a ZS in radio emission from the pulsar in the Crab nebula.

[106] arXiv:1807.08816v1 [pdf, vox]

Multi-messenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A

The IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H. E. S. S, INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool telescope, Subaru, Swift/NuSTAR, VERITAS, VLA/17B-403 teams
Submitted Monday 23 July 2018 @ 20:33:59 GMT

Individual astrophysical sources previously detected in neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017 we detected a high-energy neutrino, IceCube-170922A, with an energy of approximately 290 TeV. Its arrival direction was consistent with the location of a known gamma-ray blazar TXS 0506+056, observed to be in a flaring state. An extensive multi-wavelength campaign followed, ranging from radio frequencies to gamma-rays. These observations characterize the variability and energetics of the blazar and include the first detection of TXS 0506+056 in very-high-energy gamma-rays. This observation of a neutrino in spatial coincidence with a gamma-ray emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

[107] arXiv:1807.08800v1 [pdf, vox]

Comment on "Understanding the $γ$-ray emission from the globular cluster 47 Tuc: evidence for dark matter?"

Richard Bartels, Thomas Edwards
Submitted Monday 23 July 2018 @ 19:33:54 GMT
4 pages, 2 figures

In a recent paper Brown et al. (2018) analyze the spectral properties of the globular cluster 47 Tucanae (47 Tuc) using 9 years of Fermi-LAT data. Brown et al. (2018) argue that the emission from 47 Tuc cannot be explained by millisecond pulsars (MSPs) alone because of a significant discrepancy between the MSP spectral properties and those of 47 Tuc. It is argued that there is a significant ($>5\sigma$) preference for a two source scenario. The second component could be from the annihilation of dark matter in a density spike surrounding the intermediate-mass black hole candidate in 47 Tuc. In this paper we argue that the claimed discrepancy arises because Brown et al. (2017) use a stacked MSP spectrum to model the emission from MSPs in 47 Tuc which is insufficient to account for the uncertainties in the spectrum of the MSPs in 47 Tuc. Contrary to the claims by Brown et al. (2018), we show that the significance of an additional dark matter component is $\lesssim 2\sigma$ when sample variance in the spectrum of a population of MSPs is accounted for. The spectrum of 47 Tuc is compatible with that of a population of MSPs similar to the disk population.

[108] arXiv:1807.08799v1 [pdf, vox]

WEIRD: Wide-orbit Exoplanet search with InfraRed Direct imaging

Frédérique Baron, Étienne Artigau, Julien Rameau, David Lafrenière, Jonathan Gagné, Lison Malo, Loïc Albert, Marie-Eve Naud, René Doyon, Markus Janson, Philippe Delorme, Charles Beichman
Submitted Monday 23 July 2018 @ 19:33:46 GMT
55 pages, 16 figures, accepted to AJ

We report results from the Wide-orbit Exoplanet search with InfraRed Direct imaging (WEIRD), a survey designed to search for Jupiter-like companions on very wide orbits (1000 to 5000 AU) around young stars ($<$120 Myr) that are known members of moving groups in the solar neighborhood ($<$70 pc). Sharing the same age, distance, and metallicity as their host while being on large enough orbits to be studied as "isolated" objects make such companions prime targets for spectroscopic observations and valuable benchmark objects for exoplanet atmosphere models. The search strategy is based on deep imaging in multiple bands across the near-infrared domain. For all 177 objects of our sample, $z_{ab}^\prime$, $J$, [3.6] and [4.5] images were obtained with CFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and $Spitzer$/IRAC. Using this set of 4 images per target, we searched for sources with red $z_{ab}^\prime$ and $[3.6]-[4.5]$ colors, typically reaching good completeness down to 2Mjup companions, while going down to 1Mjup for some targets, at separations of $1000-5000$ AU. The search yielded 4 candidate companions with the expected colors, but they were all rejected through follow-up proper motion observations. Our results constrain the occurrence of 1-13 Mjup planetary-mass companions on orbits with a semi-major axis between 1000 and 5000 AU at less than 0.03, with a 95\% confidence level.

[109] arXiv:1807.08794v1 [pdf, vox]

Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert

IceCube Collaboration
Submitted Monday 23 July 2018 @ 19:24:12 GMT

A high-energy neutrino event detected by IceCube on 22 September 2017 was coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056. Prompted by this association, we investigated 9.5 years of IceCube neutrino observations to search for excess emission at the position of the blazar. We found an excess of high-energy neutrino events with respect to atmospheric backgrounds at that position between September 2014 and March 2015. Allowing for time-variable flux, this constitutes 3.5{\sigma} evidence for neutrino emission from the direction of TXS 0506+056, independent of and prior to the 2017 flaring episode. This suggests that blazars are the first identifiable sources of the high-energy astrophysical neutrino flux.

[110] arXiv:1807.09593v1 [pdf, vox]

Self-organization of solar magnetic fields

T. R. Jarboe, T. E. Benedett, C. J. Everson, C. J. Hansen, A. C. Hossack, K. D. Morgan, B. A. Nelson, J. M. Penna, D. A. Sutherland
Submitted Monday 23 July 2018 @ 18:33:11 GMT
arXiv admin note: substantial text overlap with arXiv:1712.01247

Self-organization properties of sustained magnetized plasma are applied to selected solar data to understand solar magnetic fields. Torsional oscillations are speed-up and slow-down bands of the azimuthal flow that correlate with the solar cycle, and they imply the existence of a symmetric solar dynamo with a measured polar flux of 3x10^14 Wb. It is shown that the solar dynamo is thin (~0.1 Mm gradient scale size) and powerful (~10^23 W). These properties are found from the amplitude of the torsional oscillations and the relationship of their velocity contours to solar magnetograms supports the result. The dynamo has enough power to heat the chromosphere and to power the corona and the solar wind. The dynamo also causes a rigid rotation of the heliosphere out to at least the corona and the relationship of the rotation of the corona to solar magnetograms supports this result as well. The thin solar dynamo sustains a thin stable minimum energy state that seems to be covering most of the solar surface just below the photosphere. The magnetic field lines of the minimum energy state should be parallel to the solar surface and rotate with distance from the surface with 2{\pi} radians of rotation in ~1 Mm Resistive diffusion helps to push the magnetic fields to the surface and the global magnetic structure (GMS) seems to lose {\pi} radians every 11 years, causing the observed 180 degree flipping of the solar magnetic field. The thin sheets of magnetized plasma in solar prominences may be the lost thin sheets of the GMS. For completeness, the formation of sunspots, CMEs and flares is discussed.

[111] arXiv:1807.08769v1 [pdf, vox]

Outer Solar System Exploration: A Compelling and Unified Dual Mission Decadal Strategy for Exploring Uranus, Neptune, Triton, Dwarf Planets, and Small KBOs and Centaurs

Amy A. Simon, S. Alan Stern, Mark Hofstadter
Submitted Monday 23 July 2018 @ 18:01:16 GMT

Laying the Vision and Voyages (V&V, National Research Council 2011) Decadal Survey 2013-2022 objectives against subsequent budget profiles reveals that separate missions to every desirable target in the Solar System are simply not realistic. In fact, very few of these missions will be achievable under current budget realities. Given the cost and difficulty in reaching the outer Solar System, competition between high-value science missions to an Ice Giant system and the Kuiper Belt is counterproductive. A superior approach is to combine the two programs into an integrated strategy that maximizes the science that can be achieved across many science disciplines and communities, while recognizing pragmatic budget limitations.

[112] arXiv:1807.08766v1 [pdf, vox]

Enhanced Rotational Mixing in the Radiative Zones of Massive Stars

Adam S. Jermyn, Christopher A. Tout, Shashikumar M. Chitre
Submitted Monday 23 July 2018 @ 18:00:29 GMT
21 pages, 10 figures. Accepted in MNRAS

Convection in the cores of massive stars becomes anisotropic when they rotate. This anisotropy leads to a misalignment of the thermal gradient and the thermal flux, which in turn results in baroclinicity and circulation currents in the upper radiative zone. We show that this induces a much stronger meridional flow in the radiative zone than previously thought. This drives significantly enhanced mixing, though this mixing does not necessarily reach the surface. The extra mixing takes on a similar form to convective overshooting, and is relatively insensitive to the rotation rate above a threshold, and may help explain the large overshoot distances inferred from observations. This has significant consequences for the evolution of these stars by enhancing core-envelope mixing.

[113] arXiv:1807.08765v1 [pdf, vox]

Stellar populations and star formation histories of the nuclear star clusters in six nearby galaxies

Nikolay Kacharov, Nadine Neumayer, Anil C. Seth, Michele Cappellari, Richard McDermid, C. Jakob Walcher, Torsten Böker
Submitted Monday 23 July 2018 @ 18:00:28 GMT
Accepted for publication in MNRAS

The majority of spiral and elliptical galaxies in the Universe host very dense and compact stellar systems at their centres known as nuclear star clusters (NSCs). In this work we study the stellar populations and star formation histories (SFH) of the NSCs of six nearby galaxies with stellar masses ranging between $2$ and $8\times10^9~{\rm M_{\odot}}$ (four late-type spirals and two early-types) with high resolution spectroscopy. Our observations are taken with the X-Shooter spectrograph at the VLT. We make use of an empirical simple stellar population (SSP) model grid to fit composite stellar populations to the data and recover the SFHs of the nuclei. We find that the nuclei of all late-type galaxies experienced a prolonged SFH, while the NSCs of the two early-types are consistent with SSPs. The NSCs in the late-type galaxies sample appear to have formed a significant fraction of their stellar mass already more than $10$ Gyr ago, while the NSCs in the two early-type galaxies are surprisingly younger. Stars younger than $100$ Myr are present in at least two nuclei: NGC 247 and NGC 7793, with some evidence for young star formation in NGC 300's NSC. The NSCs of the spirals NGC 247 and NGC 300 are consistent with prolonged \in situ star formation with a gradual metallicity enrichment from $\sim-1.5$ dex more than $10$ Gyr ago, reaching super-Solar values few hundred Myr ago. NGC 3621 appears to be very metal rich already in the early Universe and NGC 7793 presents us with a very complex SFH, likely dominated by merging of various massive star clusters coming from different environments.

[114] arXiv:1807.08762v1 [pdf, vox]

A wildly flickering jet in the black hole X-ray binary MAXI J1535-571

M. C. Baglio, D. M. Russell, P. Casella, H. Al Noori, A. Al Yazeedi, T. Belloni, D. A. H. Buckley, M. Cadolle Bel, C. Ceccobello, S. Corbel, F. Coti Zelati, M. Diaz Trigo, R. P. Fender, E. Gallo, P. Gandhi, J. Homan, K. I. I. koljonen, F. lewis, T. J. Maccarone, J. Malzac, S. Markoff, J. C. A. Miller-Jones, K. O'Brien, T. D. Russell, P. Saikia, T. Shahbaz, G. R. Sivakoff, R. Soria, V. Testa, A. J. Tetarenko, M. E. van den Ancker, F. M. Vincentelli
Submitted Monday 23 July 2018 @ 18:00:05 GMT
18 pages, 8 figures. Submitted to ApJ, comments welcome

We report on the results of optical, near-infrared (NIR) and mid-infrared observations of the black hole X-ray binary candidate (BHB) MAXI J1535-571 during its 2017/2018 outburst. During the first part of the outburst (MJD 58004-58012), the source shows an optical-NIR spectrum that is consistent with an optically thin synchrotron power-law from a jet. After MJD 58015, however, the source faded considerably, the drop in flux being much more evident at lower frequencies. Before the fading, we measure a de-reddened flux density of $\gtrsim$100 mJy in the mid-infrared, making MAXI J1535-571 one of the brightest mid-infrared BHBs known so far. A significant softening of the X-ray spectrum is evident contemporaneous with the infrared fade. We interpret it as due to the suppression of the jet emission, similar to the accretion-ejection coupling seen in other BHBs. However, MAXI J1535-571 did not transition smoothly to the soft state, instead showing X-ray hardness deviations, associated with infrared flaring. We also present the first mid-IR variability study of a BHB on minute timescales, with a fractional rms variability of the light curves of $\sim 15-22 \%$, which is similar to that expected from the internal shock jet model, and much higher than the optical fractional rms ($\lesssim 7 \%$). These results represent an excellent case of multi-wavelength jet spectral-timing and demonstrate how rich, multi-wavelength time-resolved data of X-ray binaries over accretion state transitions can help refining models of the disk-jet connection and jet launching in these systems.

[115] arXiv:1807.08761v1 [pdf, vox]

The role of mergers in driving morphological transformation over cosmic time

G. Martin, S. Kaviraj, J. E. G. Devriendt, Y. Dubois, C. Pichon
Submitted Monday 23 July 2018 @ 18:00:04 GMT
Accepted for publication in MNRAS

Understanding the processes that trigger morphological transformation is central to understanding how and why the Universe transitions from being disc-dominated at early epochs to having the morphological mix that is observed today. We use Horizon-AGN, a cosmological hydrodynamical simulation, to perform a comprehensive study of the processes that drive morphological change in massive (M > 10^10 MSun) galaxies over cosmic time. We show that (1) essentially all the morphological evolution in galaxies that are spheroids at z=0 is driven by mergers with mass ratios greater than 1:10, (2) major mergers alone cannot produce today's spheroid population -- minor mergers are responsible for a third of all morphological transformation over cosmic time and are its dominant driver after z~1, (3) prograde mergers trigger milder morphological transformation than retrograde mergers -- while both types of events produce similar morphological changes at z>2, the average change due to retrograde mergers is around twice that due to their prograde counterparts at z~0, (4) remnant morphology depends strongly on the gas fraction of a merger, with gas-rich mergers routinely re-growing discs, and (5) at a given stellar mass, discs do not exhibit drastically different merger histories from spheroids -- disc survival in mergers is driven by acquisition of cold gas (via cosmological accretion and gas-rich interactions) and a preponderance of prograde mergers in their merger histories.

[116] arXiv:1807.08758v1 [pdf, vox]

Clustered Supernovae Drive Powerful Galactic Winds After Super-Bubble Breakout

Drummond Fielding, Eliot Quataert, Davide Martizzi
Submitted Monday 23 July 2018 @ 18:00:02 GMT
19 pages, 12 figures, and 3 page appendix with 6 figures. Movies available at http://w.astro.berke​ley.edu/~dfielding/#​SNeDrivenWinds/

We use three-dimensional hydrodynamic simulations of vertically stratified patches of galactic discs to study how the spatio-temporal clustering of supernovae (SNe) enhances the power of galactic winds. SNe that are randomly distributed throughout a galactic disc drive inefficient galactic winds because most supernova remnants lose their energy radiatively before breaking out of the disc. Accounting for the fact that most star formation is clustered alleviates this problem. Super-bubbles driven by the combined effects of clustered SNe propagate rapidly enough to break out of galactic discs well before the clusters' SNe stop going off. The radiative losses post-breakout are reduced dramatically and a large fraction ($\gtrsim 0.2$) of the energy released by SNe vents into the halo powering a strong galactic wind. These energetic winds are capable of providing strong preventative feedback and eject substantial mass from the galaxy with outflow rates on the order of the star formation rate. The momentum flux in the wind is only of order that injected by the SNe, because the hot gas vents before doing significant work on the surroundings. We show that our conclusions hold for a range of galaxy properties, both in the local Universe (e.g., M82) and at high redshift (e.g., $z \sim 2$ star forming galaxies). We further show that if the efficiency of forming star clusters increases with increasing gas surface density, as suggested by theoretical arguments, the condition for star cluster-driven super-bubbles to break out of galactic discs corresponds to a threshold star formation rate surface density for the onset of galactic winds $\sim 0.03$ M$_\odot$ yr$^{-1}$ kpc$^{-2}$, of order that observed.

[117] arXiv:1807.08759v1 [pdf, vox]

SN Ia Standardization on the Rise: Evidence for the Cosmological Importance of Pre-Maximum Measurements

Brian Hayden, David Rubin, Mark Strovink
Submitted Monday 23 July 2018 @ 18:00:02 GMT
Submitted to ApJ

We present SALT2X, an extension of the SALT2 model for type Ia supernova light curves. SALT2X separates the light-curve-shape parameter x1 into an x1r and x1f for the rise and fall portions of the light curve. Using the Joint Lightcurve Analysis (JLA) SN sample, we assess the importance of the rising and falling portions of the light curve for cosmological standardization using a modified version of the Unified Nonlinear Inference for Type Ia cosmologY (UNITY) framework. We find strong evidence of a preference for x1r in the standardization relation. We see evidence that standardizing on the rise affects the color standardization relation, and reduces the size of the host-galaxy standardization and the unexplained ("intrinsic") luminosity dispersion. Since SNe Ia generally rise more quickly than they decline, a faster observing cadence in future surveys will be necessary to maximize the gain from this work, and to continue to explore the impacts of decoupling the rising and falling portions of SN Ia light curves.

[118] arXiv:1807.08753v1 [pdf, vox]

M31 PAndromeda Cepheid sample observed in four HST bands

Mihael Kodric, Arno Riffeser, Stella Seitz, Ulrich Hopp, Jan Snigula, Claus Goessl, Johannes Koppenhoefer, Ralf Bender
Submitted Monday 23 July 2018 @ 18:00:00 GMT
32 pages, 19 figures, 9 tables, accepted for publication in ApJ, electronic data will be available on CDS

Using the M31 PAndromeda Cepheid sample and the HST PHAT data we obtain the largest Cepheid sample in M31 with HST data in four bands. For our analysis we consider three samples: A very homogeneous sample of Cepheids based on the PAndromeda data, the mean magnitude corrected PAndromeda sample and a sample complementing the PAndromeda sample with Cepheids from literature. The latter results in the largest catalog with 522 fundamental mode (FM) Cepheids and 102 first overtone (FO) Cepheids with F160W and F110W data and 559 FM Cepheids and 111 FO Cepheids with F814W and F475W data. The obtained dispersion of the Period-Luminosity relations (PLRs) is very small (e.g. 0.138 mag in the F160W sample I PLR). We find no broken slope in the PLRs when analyzing our entire sample, but we do identify a subsample of Cepheids that causes the broken slope. However, this effect only shows when the number of this Cepheid type makes up a significant fraction of the total sample. We also analyze the sample selection effect on the Hubble constant.

[119] arXiv:1807.08750v1 [pdf, vox]

The Next Generation Virgo Cluster Survey (NGVS) XXXI. The kinematics of intra-cluster globular clusters in the core of the Virgo cluster

Alessia Longobardi, Eric W. Peng, Patrick Côté, J. Christopher Mihos, Laura Ferrarese, Thomas H. Puzia, Ariane Lançon, Hong-Xin Zhang, Roberto P. Muñoz, John P. Blakeslee, Puragra Guhathakurta, Patrick R. Durrell, Rúben Sánchez-Janssen, Elisa Toloba, Andrés Jordán, Susana Eyheramendy, Jean-Charles Cuillandre, Stephen D. J. Gwyn, Alessandro Boselli, Pierre-Alain Duc, Chengze Liu, Karla Alamo-Martínez, Mathieu Powalka, Sungsoon Lim
Submitted Monday 23 July 2018 @ 17:59:59 GMT
31 pages, 13 figures, 1 table, accepted for publication in ApJ

Intra-cluster (IC) populations are expected to be a natural result of the hierarchical assembly of clusters, yet their low space densities make them difficult to detect and study. We present the first definitive kinematic detection of an IC population of globular clusters (GCs) in the Virgo cluster, around the central galaxy, M87. This study focuses on the Virgo core for which the combination of NGVS photometry and follow-up spectroscopy allows us to reject foreground star contamination and explore GC kinematics over the full Virgo dynamical range. The GC kinematics changes gradually with galactocentric distance, decreasing in mean velocity and increasing in velocity dispersion, eventually becoming indistinguishable from the kinematics of Virgo dwarf galaxies at $\mathrm{R>320\, kpc}$. By kinematically tagging M87 halo and intra-cluster GCs we find that 1) the M87 halo has a smaller fraction ($52\pm3\%$) of blue clusters with respect to the IC counterpart ($77\pm10\%$), 2) the $(g'-r')_{0}$ vs $(i'-z')_{0}$ color-color diagrams reveal a galaxy population that is redder than the IC population that may be due to a different composition in chemical abundance and progenitor mass, and 3) the ICGC distribution is shallower and more extended than the M87 GCs, yet still centrally concentrated. The ICGC specific frequency, $S_{N,\mathrm{ICL}}=​10.2\pm4.8$, is consistent with what is observed for the population of quenched, low-mass galaxies within 1~Mpc from the cluster's center. The IC population at Virgo's center is thus consistent with being an accreted component from low-mass galaxies tidally stripped or disrupted through interactions, with a total mass of $\mathrm{M_{ICL,tot}​=10.8\pm0.1\times10^​{11}M_{\odot}}$.

[120] arXiv:1807.08749v1 [pdf, vox]

TASI Lectures on Early Universe Cosmology: Inflation, Baryogenesis and Dark Matter

James M. Cline
Submitted Monday 23 July 2018 @ 17:56:48 GMT
52 pages, 29 figures

These lectures, presented at TASI 2018, provide a concise introduction to inflation, baryogenesis, and aspects of dark matter not covered by the other lectures. The emphasis for inflation is an intuitive understanding and techniques for constraining inflationary models. For baryogenesis we focus on two examples, leptogenesis and electroweak baryogenesis, with attention to singlet-assisted two-step phase transitions. Concerning dark matter, we review different classes of models distinguished by their mechanisms for obtaining the observed relic density, including thermal freeze-out, asymmetric dark matter, freeze-in, SIMP dark matter, the misalignment mechanism for ultralight scalars and axions, and production of primordial black holes during inflation. Problem sets are provided.

[121] arXiv:1807.08740v1 [pdf, vox]

Astrophysical explanations of suspected dark matter signals in dwarf galaxies

Alex Geringer-Sameth, Savvas M. Koushiappas, Matthew G. Walker, Vincent Bonnivard, Céline Combet, David Maurin
Submitted Monday 23 July 2018 @ 17:36:06 GMT
16 pages, 5 figures, 1 table

We present methods to assess whether gamma-ray excesses towards Milky Way dwarf galaxies can be attributed to astrophysical sources rather than to dark matter annihilation. As a case study we focus on Reticulum II, the dwarf which shows the strongest evidence for a gamma-ray signal in Fermi data. Dark matter models and those with curved energy spectra provide good fits to the data, while a simple power law is ruled out at 97.5% confidence. We compare RetII's spectrum to known classes of gamma-ray sources and find a useful representation in terms of spectral curvature and the energy at which the spectral energy distribution peaks. In this space the blazar classes appear segregated from the confidence region occupied by RetII. Pulsars have similar gamma-ray spectra to RetII but we show that RetII is unlikely to host a pulsar population detectable in gamma rays. Tensions with astrophysical explanations are stronger when analyzing 6.5 years of Pass 7 than with the same amount of Pass 8 data, where the excess is less significant. These methods are applicable to any dwarf galaxy which is a promising dark matter target and shows signs of gamma-ray emission along its line of sight.

[122] arXiv:1807.08734v1 [pdf, vox]

Origins of Extragalactic Cosmic Ray Nuclei by Contracting Alignment Patterns induced in the Galactic Magnetic Field

Martin Erdmann, Lukas Geiger, David Schmidt, Martin Urban, Marcus Wirtz
Submitted Monday 23 July 2018 @ 17:32:18 GMT
14 pages, 15 figures

We present a novel approach to search for origins of ultra-high energy cosmic rays. These particles are likely nuclei that initiate extensive air showers in the Earth's atmosphere. In large-area observatories, the particle arrival directions are measured together with their energies and the atmospheric depth at which their showers maximize. The depths provide rough measures of the nuclear charges. In a simultaneous fit to all observed cosmic rays we use the galactic magnetic field as a mass spectrometer and adapt the nuclear charges such that their extragalactic arrival directions are concentrated in as few directions as possible. Using different simulated examples we show that, with the measurements on Earth, reconstruction of extragalactic source directions is possible. In particular, we show in an astrophysical scenario that source directions can be reconstructed even within a substantial isotropic background.

[123] arXiv:1807.08732v1 [pdf, vox]

Cosmological constraints from noisy convergence maps through deep learning

Janis Fluri, Tomasz Kacprzak, Aurelien Lucchi, Alexandre Refregier, Adam Amara, Thomas Hofmann
Submitted Monday 23 July 2018 @ 17:30:03 GMT
15 pages, 11 figures

Deep learning is a powerful analysis technique that has recently been proposed as a method to constrain cosmological parameters from weak lensing mass maps. Due to its ability to learn relevant features from the data, it is able to extract more information from the mass maps than the commonly used power spectrum, and thus achieve better precision for cosmological parameter measurement. We explore the advantage of Convolutional Neural Networks (CNN) over the power spectrum for varying levels of shape noise and different smoothing scales applied to the maps. We compare the cosmological constraints from the two methods in the $\Omega_M-\sigma_8$ plane for sets of 400 deg$^2$ convergence maps. We find that, for a shape noise level corresponding to 8.53 galaxies/arcmin$^2$ and the smoothing scale of $\sigma_s = 2.34$ arcmin, the network is able to generate 45% tighter constraints. For smaller smoothing scale of $\sigma_s = 1.17$ the improvement can reach $\sim 50 \%$, while for larger smoothing scale of $\sigma_s = 5.85$, the improvement decreases to 19%. The advantage generally decreases when the noise level and smoothing scales increase. We present a new training strategy to train the neural network with noisy data, as well as considerations for practical applications of the deep learning approach.

[124] arXiv:1807.08728v1 [pdf, vox]

P/2017 S5: Another Active Asteroid Associated with the Theobalda Family

Bojan Novakovic
Submitted Monday 23 July 2018 @ 17:22:42 GMT

In this note we have shown that a newly discovered comet P/2017 S5 (ATLAS), that moves around the Sun in an asteroid-like orbit, is a member of the Theobalda asteroid family.

[125] arXiv:1807.08726v1 [pdf, vox]

Universal Afterglow Of Supernova-Less Gamma Ray Bursts

Shlomo Dado, Arnon Dar
Submitted Monday 23 July 2018 @ 17:20:36 GMT
Comments are welcome

The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born milli second pulsar.

[126] arXiv:1807.08752v1 [pdf, vox]

New Galactic Planetary Nebulae selected by radio and multi-wavelength characteristics

Vasiliki Fragkou, Quentin A. Parker, Ivan S. Bojicic, Nazim Aksaker
Submitted Monday 23 July 2018 @ 17:09:26 GMT
13 pages, 5 figures

We have used the Cornish radio catalogue combined with the use of multi-wavelength data to identify 62 new Planetary Nebula (PN) candidates close to the Galactic mid-plane. Of this sample 11 have weak optical counterparts in deep narrow band H$\alpha$ imaging that allows their spectroscopic follow-up. We have observed eight of these candidates spectroscopically, leading to the confirmation of 7 out of 8 as PNe. All but one of our sample of newly detected PNe appear to be of Type I chemistry with very large [NII]/H$\alpha$ ratios. This indicates that our selection method heavily favours detection of this kind of PN. Cornish is a low Galactic latitude survey where young objects and Type I PNe (thought to derive from higher mass progenitors) are more plentiful, but where optical extinction is large. The very high success rate in correctly identifying PNe in this zone proves the efficacy of our radio and multiple multi-wavelength diagnostic tools used to successfully predict and then confirm their PN nature, at least in the cases where an optical counterpart is found and has been observed. The study reinforces the effective use of a combination of multi-wavelength and optical data in the identification of new Galactic PNe and especially those of Type I chemistries whose dusty environments often prevents their easy detection in the optical regime alone.

[127] arXiv:1807.08710v1 [pdf, vox]

Maunakea Spectroscopic Explorer (MSE): a preliminary design of multi-object high resolution spectrograph

Kai Zhang, Yifei Zhou, Zhen Tang, Will Saunders, Kim A. Venn, Jianrong Shi, Alan W. McConnachie, Kei Szeto, Lei Wang, Yongtian Zhu, Zhongwen Hu
Submitted Monday 23 July 2018 @ 16:38:40 GMT
15 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

The Maunakea Spectroscopic Explorer (MSE) project will transform the CFHT 3.6m optical telescope to a 10m class dedicated multi-object spectroscopic facility, with an ability to measure thousands of objects with three spectral resolution modes respectively low resolution of R~3,000, moderate resolution of R~6,000 and high resolution of R~40,000. Two identical multi-object high resolution spectrographs are expected to simultaneously produce 1084 spectra with high resolution of 40,000 at Blue (401-416nm) and Green (472-489nm) channels, and 20,000 at Red (626-674nm) channel. At the Conceptual Design Phase (CoDP), different optical schemes were proposed to meet the challenging requirements, especially a unique design with a novel transmission image slicer array, and another conventional design with oversize Volume Phase Holographic (VPH) gratings. It became clear during the CoDP that both designs presented problems of complexity or feasibility of manufacture, especially high line density disperser (general name for all kinds of grating, grism, prism). At the present, a new design scheme is proposed for investigating the optimal way to reduce technical risk and get more reliable estimation of cost and timescale. It contains new dispersers, F/2 fast collimator and so on. Therein, the disperser takes advantage of a special grism and a prism to reduce line density on grating surface, keep wide opening angle of optical path, and get the similar spectrum layout in all three spectral channels. For the fast collimator, it carefully compares on-axis and off-axis designs in throughput, interface to fiber assembly and technical risks. The current progress is more competitive and credible than the previous design, but it also indicates more challenging work will be done to improve its accessibility in engineering.

[128] arXiv:1807.09179v1 [pdf, vox]

Maunakea Spectroscopic Explorer Low Moderate Resolution Spectrograph Conceptual Design

Patrick Caillier, Will Saunders, Pierre-Henri Carton, Florence Laurent, Jean-Emmanuel Migniau, Arlette Pécontal, Johan Richard, Christophe Yèche
Submitted Monday 23 July 2018 @ 16:35:16 GMT
20 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

The Maunakea Spectroscopic Explorer (MSE) Project is a planned replacement for the existing 3.6-m Canada France Hawaii Telescope (CFHT) into a 10-m class dedicated wide field highly multiplexed fibre fed spectroscopic facility. MSE seeks to tackle basic science questions ranging from the origin of stars and stellar systems, Galaxy archaeology at early times, galaxy evolution across cosmic time, to cosmology and the nature of dark matter and dark energy. MSE will be a primary follow-up facility for many key future photometric and astrometric surveys, as well as a major component in the study of the multi-wavelength Universe. The MSE is based on a prime focus telescope concept which illuminate 3200 fibres or more. These fibres are feeding a Low Moderate Resolution (LMR) spectrograph and a High Resolution (HR). The LMR will provide 2 resolution modes at R>2500 and R>5000 on a wavelength range of 360 to 950 nm and a resolution of R>3000 on the 950 nm to 1300 nm bandwidth. Possibly the H band will be also covered by a second NIR mode from ranging from 1450 to 1780 nm. The HR will have a resolution of R>39000 on the 360 to 600 nm wavelength range and R>20000 on the 600 to 900 nm bandwidth. This paper presents the LMR design after its Conceptual Design Review held in June 2017. It focuses on the general concept, optical and mechanical design of the instrument. It describes the associated preliminary expected performances especially concerning optical and thermal performances.

[129] arXiv:1807.08687v1 [pdf, vox]

SPOTS: The Search for Planets Orbiting Two Stars. III. Complete Sample and Statistical Analysis

Ruben Asensio-Torres, Markus Janson, Mariangela Bonavita, Silvano Desidera, Christian Thalmann, Masayuki Kuzuhara, Thomas Henning, Francesco Marzari, Michael R. Meyer, Per Calissendorff, Taichi Uyama
Submitted Monday 23 July 2018 @ 15:56:35 GMT
27 pages, 13 Figures, 7 Tables. Accepted for publication in A&A

Binary stars constitute a large percentage of the stellar population, yet relatively little is known about the planetary systems orbiting them. Most constraints on circumbinary planets (CBPs) so far come from transit observations with the Kepler telescope, which is sensitive to close-in exoplanets but does not constrain planets on wider orbits. However, with continuous developments in high-contrast imaging techniques, this population can now be addressed through direct imaging. We present the full survey results of the Search for Planets Orbiting Two Stars (SPOTS) survey, which is the first direct imaging survey targeting CBPs. The SPOTS observational program comprises 62 tight binaries that are young and nearby, and thus suitable for direct imaging studies, with VLT/NaCo and VLT/SPHERE. Results from SPOTS include the resolved circumbinary disk around AK Sco, the discovery of a low-mass stellar companion in a triple packed system, the relative astrometry of up to 9 resolved binaries, and possible indications of non-background planetary-mass candidates around HIP 77911. We did not find any CBP within 300 AU, which implies a frequency upper limit on CBPs (1--15 $M_{\rm Jup}$) of 6--10 % between 30-300 AU. Coupling these observations with an archival dataset for a total of 163 stellar pairs, we find a best-fit CBP frequency of 1.9 % (2--15 $M_{\rm Jup}$) between 1--300 AU with a 10.5 % upper limit at a 95 % confidence level. This result is consistent with the distribution of companions around single stars.

[130] arXiv:1807.08653v1 [pdf, vox]

The XXL Survey: XXXIV. Double irony in XXL-North. A tale of two radio galaxies in a supercluster at z = 0.14

C. Horellou, H. T. Intema, V. Smolčić, A. Nilsson, F. Karlsson, C. Krook, L. Tolliner, C. Adami, C. Benoist, M. Birkinshaw, C. Caretta, L. Chiappetti, J. Delhaize, C. Ferrari, S. Fotopoulou, V. Guglielmo, K. Kolokythas, F. Pacaud, M. Pierre, B. M. Poggianti, M. E. Ramos-Ceja, S. Raychaudhury, H. J. A. Röttgering, C. Vignali
Submitted Monday 23 July 2018 @ 14:54:31 GMT
23 pages, 16 figures, accepted for publication in A&A

We show how the XXL multiwavelength survey can be used to shed light on radio galaxies and their environment. Two prominent radio galaxies were identified in a visual examination of the mosaic of XXL-North obtained with the Giant Metrewave Radio Telescope at 610MHz. Counterparts were searched for in other bands. Spectroscopic redshifts from the GAMA database were used to identify clusters and/or groups of galaxies, estimate their masses with the caustic method, and quantify anisotropies in the surrounding galaxy distribution via a Fourier analysis. Both radio galaxies are of FR I type and are hosted by early-type galaxies at a redshift of 0.138. The first radio source, named the Exemplar, has a physical extent of about 400 kpc; it is located in the cluster XLSSC112, which has a temperature of about 2 keV, a total mass of about $10^{14} M_\odot$, and resides in an XXL supercluster with eight known members. The second source, named the Double Irony, is a giant radio galaxy with a total length of about 1.1 Mpc. Its core coincides with a cataloged point-like X-ray source, but no extended X-ray emission from a surrounding galaxy cluster was detected. However, from the optical data we determined that the host is the brightest galaxy in a group that is younger, less virialized, and less massive than the Exemplar's cluster. A friends-of-friends analysis showed that the Double Irony's group is a member of the same supercluster as the Exemplar. There are indications that the jets and plumes of the Double Irony have been deflected by gas associated with the surrounding galaxy distribution. Another overdensity of galaxies (the tenth) containing a radio galaxy was found to be associated with the supercluster. Radio galaxies can be used to find galaxy clusters/groups that are below the current sensitivity of X-ray surveys.

[131] arXiv:1807.08637v1 [pdf, vox]

MUSCAT: The Mexico-UK Sub-Millimetre Camera for AsTronomy

Thomas L. R. Brien, Peter A. R. Ade, Peter S. Barry, Edgar Castillo-Domìnguez, Daniel Ferrusca, Thomas Gascard, Victor Gómez, Peter C. Hargrave, Amber L. Hornsby, David Hughes, Enzo Pascale, Josie D. A. Parrianen, Abel Perez, Sam Rowe, Carole Tucker, Salvador Ventura González, Simon M. Doyle
Submitted Monday 23 July 2018 @ 14:25:56 GMT
Presented at SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

The Mexico-UK Sub-millimetre Camera for AsTronomy (MUSCAT) is a large-format, millimetre-wave camera consisting of 1,500 background-limited lumped-element kinetic inductance detectors (LEKIDs) scheduled for deployment on the Large Millimeter Telescope (Volc\'an Sierra Negra, Mexico) in 2018. MUSCAT is designed for observing at 1.1 mm and will utilise the full 40' field of view of the LMTs upgraded 50-m primary mirror. In its primary role, MUSCAT is designed for high-resolution follow-up surveys of both galactic and extra-galactic sub-mm sources identified by Herschel. MUSCAT is also designed to be a technology demonstrator that will provide the first on-sky demonstrations of novel design concepts such as horn-coupled LEKID arrays and closed continuous cycle miniature dilution refrigeration. Here we describe some of the key design elements of the MUSCAT instrument such as the novel use of continuous sorption refrigerators and a miniature dilutor for continuous 100-mK cooling of the focal plane, broadband optical coupling to Aluminium LEKID arrays using waveguide chokes and anti-reflection coating materials as well as with the general mechanical and optical design of MUSCAT. We explain how MUSCAT is designed to be simple to upgrade and the possibilities for changing the focal plane unit that allows MUSCAT to act as a demonstrator for other novel technologies such as multi-chroic polarisation sensitive pixels and on-chip spectrometry in the future. Finally, we will report on the current status of MUSCAT's commissioning.

[132] arXiv:1807.08600v1 [pdf, vox]

X-ray spectral variability of blazars using principal component analysis

Dennis Gallant, Luigi C. Gallo, Michael L. Parker
Submitted Monday 23 July 2018 @ 13:32:29 GMT
13 pages, 7 figures, accepted for publication in MNRAS

Principal Component Analysis (PCA) is applied to a variety of blazars to examine X-ray spectral variability. Data from nine different objects are analysed in two ways: long-term, which examines variability trends across years or decades, and short-term, which looks at variability within a single observation. The results are then compared to simulated spectra in order to identify the physical components that they correspond to. It is found that long-term variability for all objects is dominated by changes in a single power law component. The primary component is responsible for more than 84 per cent of the variability in every object, while the second component is responsible for at least 3 per cent. Small differences in the shapes of these components can be used to predict qualities such as the degree to which spectral parameters are varying relative to one another, and correlations between spectral hardness and flux. Short-term variability is less clear-cut, with no obvious physical analogue for some of the PCA results. We discuss the simulation process, and specifically remark on the consequences of the breakdown of the linearity assumption of PCA and how it manifests in the real data. We conclude that PCA is a useful tool for analysing variability, but only if its underlying assumptions and limitations are understood.

[133] arXiv:1807.07933v2 [pdf, vox]

A high dust emissivity index beta for a CO-faint galaxy in a filamentary Lyman-alpha nebula at z=3.1

Yuta Kato, Yuichi Matsuda, Daisuke Iono, Bunyo Hatsukade, Hideki Umehata, Kotaro Kohno, David M. Alexander, Yiping Ao, Scott C. Chapman, Matthew Hayes, Mariko Kubo, Bret D. Lehmer, Matthew A. Malkan, Tomonari Michiyama, Tohru Nagao, Tomoki Saito, Ichi Tanaka, Yoshiaki Taniguchi
Submitted Monday 23 July 2018 @ 13:29:47 GMT
6 pagers, 3 figures

We present CO J=4-3 line and 3 mm dust continuum observations of a 100 kpc-scale filamentary Ly{\alpha} nebula (SSA22 LAB18) at z=3.1 using the Atacama Large Millimeter/submillim​eter Array (ALMA). We detected the CO J=4-3 line at a systemic z(CO)=3.093 {\pm} 0.001 at 11 {\sigma} from one of the ALMA continuum sources associated with the Ly{\alpha} filament. We estimated the CO J=4-3 luminosity of L'CO(4-3)=(2.3\pm0.2​)x10^9 K km s^{-1} pc^2 for this CO source, which is one order of magnitude smaller than those of typical z>1 dusty star-forming galaxies (DSFGs) of similar far-infrared luminosity L(IR)~10^{12} Lsun. We derived a molecular gas mass of Mgas=(4.4^{+0.9}_{-0​.6})x10^9 Msun and a star-formation rate of SFR=270\pm160 Msun yr^{-1}. We also estimated a gas depletion time of {\tau}(dep)=17\pm10 Myr, being shorter than those of typical DSFGs. It is suggested that this source is in a transition phase from DSFG to a gas-poor, early-type galaxy. From ALMA to Herschel multi-band dust continuum observations, we measured a dust emissivity index {\beta}=2.3\pm0.2, which is similar to those of local gas-poor, early-type galaxies. Such a high {\beta} can be reproduced by specific chemical compositions for interstellar dust at the submillimeter wavelengths from recent laboratory experiments. ALMA CO and multi-band dust continuum observations can constrain the evolutionary stage of high-redshift galaxies through {\tau}(dep) and {\beta}, and thus we can investigate dust chemical compositions even in the early Universe.

[134] arXiv:1807.08594v1 [pdf, vox]

Preserving Kerr symmetries in deformed spacetimes

Georgios O. Papadopoulos, Kostas D. Kokkotas
Submitted Monday 23 July 2018 @ 13:25:27 GMT
9 pages

We present a novel approach in constructing deviations of the Kerr spacetime whereas the symmetries can be preserved. The method was applied trivially in all known classical black-hole spacetimes tested, while provides the possibility of testing and inventing deformations of Kerr in a quick and innovative way. The methodology is based on earlier work by Benenti and Francaviglia (1979) on separability of geodesic equations while we exploited the elegant properties of Yano tensor in order to provide an additional way of getting the Carter constant.

[135] arXiv:1807.08592v1 [pdf, vox]

Investigating the Rotational Phase of Stellar Flares on M dwarfs Using K2 Short Cadence Data

L. Doyle, G. Ramsay, J. G. Doyle, K. Wu, E. Scullion
Submitted Monday 23 July 2018 @ 13:19:06 GMT
Accepted main Journal MNRAS

We present an analysis of K2 short cadence data of 34 M dwarfs which have spectral types in the range M0 - L1. Of these stars, 31 showed flares with a duration between $\sim$10-90 min. Using distances obtained from Gaia DR2 parallaxes, we determined the energy of the flares to be in the range $\sim1.2\times10^{29​}-6\times10^{34}$ erg. In agreement with previous studies we find rapidly rotating stars tend to show more flares, with evidence for a decline in activity in stars with rotation periods longer than $\sim$10 days. The rotational modulation seen in M dwarf stars is widely considered to result from a starspot which rotates in and out of view. Flux minimum is therefore the rotation phase where we view the main starspot close to the stellar disk center. Surprisingly, having determined the rotational phase of each flare in our study we find none show any preference for rotational phase. We outline three scenarios which could account for this unexpected finding. The relationship between rotation phase and flare rate will be explored further using data from wide surveys such as NGTS and TESS.

[136] arXiv:1807.08565v1 [pdf, vox]

The Cryogenic AntiCoincidence detector for ATHENA X-IFU: improvement of the test setup towards the Demonstration Model

Matteo D'Andrea, Claudio Macculi, Andrea Argan, Simone Lotti, Gabriele Minervini, Luigi Piro, Michele Biasotti, Dario Corsini, Flavio Gatti, Guido Torrioli, Angela Volpe
Submitted Monday 23 July 2018 @ 12:40:34 GMT
Accepted for publication in the Journal of Low Temperature Physics for LTD-17 special issue

The ATHENA X-IFU development program foresees to build and characterize an instrument Demonstration Model (DM), in order to probe the system critical technologies before the mission adoption. In this respect, we are now developing the DM of the X-IFU Cryogenic Anticoincidence Detector (CryoAC), which will be delivered to the Focal Plane Assembly (FPA) development team for the integration with the TES array. Before the delivery, we will characterize and test the CryoAC DM in our CryoLab at INAF/IAPS. In this paper we report the main results of the activities performed to improve our cryogenic test setup, making it suitable for the DM integration. These activities mainly consist in the development of a mechanichal setup and a cryogenic magnetic shielding system, whose effectiveness has been assessed by FEM simulations and a measurement at warm. The preliminary performance test has been performed by means of the last CryoAC single pixel prototype, the AC-S8 pre-DM sample.

[137] arXiv:1807.08561v1 [pdf, vox]

The Cryogenic AntiCoincidence detector for ATHENA X-IFU: assessing the role of the athermal phonons collectors in the AC-S8 prototype

Matteo D'Andrea, Claudio Macculi, Andrea Argan, Simone Lotti, Gabriele Minervini, Luigi Piro, Michele Biasotti, Dario Corsini, Flavio Gatti, Guido Torrioli
Submitted Monday 23 July 2018 @ 12:34:36 GMT
Accepted for publication in the Journal of Low Temperature Physics for LTD-17 special issue

The ATHENA X-ray Observatory is the second large-class mission in the ESA Cosmic Vision 2015-2025 science programme. One of the two on-board instruments is the X-IFU, an imaging spectrometer based on a large array of TES microcalorimeters. To reduce the particle-induced background, the spectrometer works in combination with a Cryogenic Anticoincidence detector (CryoAC), placed less than 1 mm below the TES array. The last CryoAC single-pixel prototypes, namely AC-S7 and AC-S8, are based on large area (1 cm2) Silicon absorbers sensed by 65 parallel-connected iridium TES. This design has been adopted to improve the response generated by the athermal phonons, which will be used as fast anticoincidence flag. The latter sample is featured also with a network of Aluminum fingers directly connected to the TES, designed to further improve the athermals collection efficiency. In this paper we will report the main results obtained with AC-S8, showing that the additional fingers network is able to increase the energy collected from the athermal part of the pulses (from the 6% of AC-S7 up to the 26 % with AC-S8). Furthermore, the finger design is able to prevent the quasiparticle recombination in the aluminum, assuring a fast pulse rising front (L/R limited). In our road map, the AC-S8 prototype is the last step before the development of the CryoAC Demonstration Model (DM), which will be the detector able to demonstrate the critical technologies expected in the CryoAC development programme.

[138] arXiv:1807.08548v1 [pdf, vox]

Highest Energy Proton-Nucleus Cross Sections

Leo Stodolsky
Submitted Monday 23 July 2018 @ 11:56:39 GMT
five pages, one figure

The description of very high energy proton-proton cross sections in terms of a `black disc' with an `edge' allows of a simple generalization to highest energy proton-nucleus cross sections. This results in a leading $ln^2W$ term and a $ln\, W$ term whose coefficient depends linearly on the radius of the nucleus ($W$ the c.m. energy). The necessary parameters are determined from the fits to p-p data. Since the coefficient of the $ln W$ term is rather large, it is doubtful that the regime of $ln^2W$ dominance can be reached with available energies in accelerators or cosmic rays. However, the $ln W$ term can be relevant for highest energy cosmic rays in the atmosphere, where a large increase for the cross section on nitrogen is expected. Tests of the theory should be possible by studying the coefficient of $ln W$ at p-nucleus colliders.

[139] arXiv:1807.08541v1 [pdf, vox]

Dark Matter in Galaxies: evidences and challenges

Paolo Salucci
Submitted Monday 23 July 2018 @ 11:39:39 GMT
21 pages, 16 Figures. Based on an invited review at the Lemaitre Workshop (9-12 May 2017, Vatican Observatory). To appear on Foundation of Physics, 2018. Comments welcome

The evidence of the phenomenon for which, in galaxies, the gravitating mass is distributed differently than the luminous mass, increases as new data become available. Furthermore, this discrepancy is well structured and it depends on the magnitude and the compactness of the galaxy and on the radius, in units of its luminous size $R_{opt}$, where the measurement is performed. For the disk systems with $-13\geq M_I\geq -24$ all this leads to an amazing scenario, revealed by the investigation of individual and coadded rotation curves, according to which, the circular velocity follows, from their centers out to their virial radii, an universal profile $V_{URC} (r/R_{opt}, M_I)$ function only of the properties of the luminous mass component. Moreover, from the Universal Rotation Curve, so as from many individual high-quality RCs, we discover that, in the innermost regions of galaxies, the DM halo density profiles are very shallow. Finally, the disk mass, the central halo density and its core radius, come out all related to each other and to two properties of the distribution of light in galaxies: the luminosity and the compactness. This phenomenology, being absent in the simplest $\Lambda CDM$ Cosmology scenario, poses serious challenges to the latter or, alternatively, it requires a substantial and tuned involvement of baryons in the formation of the galactic halos. On the other side, the URC helps to explain the two-accelerations relationship found by McGaugh et al 2016, in terms of only well known astrophysical processes, acting in a standard DM halos + luminous disks scenario

[140] arXiv:1807.08528v1 [pdf, vox]

Radio pulsars: already fifty years!

V. S. Beskin
Submitted Monday 23 July 2018 @ 11:00:22 GMT
34 pages, 25 figures, typos in Eqns (100), (103) are eliminated

Although fifty years have passed since the discovery of radio pulsars, there is still no satisfactory understanding of how these amazing objects operate. While there has been significant progress in understanding the basic properties of radio pulsars, there is as yet no consensus on key issues, such as the nature of coherent radio emission or the conversion mechanism of the electromagnetic energy of the pulsar wind into particle energy. In this review, we present the main theoretical results on the magnetosphere of neutron stars. We formulate a number of apparently simple questions, which nevertheless remain unanswered since the very beginning of the field and which must be resolved before any further progress can be made.

[141] arXiv:1807.08525v1 [pdf, vox]

A multi-wavelength view of magnetic flaring from PMS stars

E. Flaccomio, G. Micela, S. Sciortino, A. M. Cody, M. G. Guarcello, M. Morales-Calderòn, L. Rebull, J. R. Stauffer
Submitted Monday 23 July 2018 @ 10:57:03 GMT
16 pages (36 including appendixes), 8 figures (main text), accepted for publication by Astronomy & Astrophysics (section 8)

Flares from the Sun and other stars are most prominently observed in the soft X-ray band. Most of the radiated energy, however, is released at optical/UV wavelengths. In spite of decades of investigation, the physics of flares is not fully understood. Even less is known about the powerful flares routinely observed from pre-main sequence stars, which might significantly influence the evolution of circumstellar disks. Observations of the NGC2264 star forming region were obtained in Dec. 2011, simultaneously with three telescopes, Chandra (X-rays), CoRoT (optical), and Spitzer (mIR), as part of the "Coordinated Synoptic Investigation of NGC2264" (CSI-NGC2264). Shorter Chandra and CoRoT observations were also obtained in March 2008. We analyzed the lightcurves to detect X-ray flares with an optical and/or mIR counterpart. Basic flare properties from the three datasets, such as emitted energies and peak luminosities, were then compared to constrain the spectral energy distribution of the flaring emission and the physical conditions of the emitting regions. Flares from stars with and without circumstellar disks were also compared to establish any difference that might be attributed to the presence of disks. Seventy-eight X-ray flares with an optical and/or mIR counterpart were detected. Their optical emission is found to correlate well with, and to be significantly larger than, the X-ray emission. The slopes of the correlations suggest that the difference becomes smaller for the most powerful flares. The mIR flare emission seems to be strongly affected by the presence of a circumstellar disk: flares from stars with disks have a stronger mIR emission with respect to stars without disks. This might be attributed to the reprocessing of the optical (and X-ray) flare emission by the inner circumstellar disk, providing evidence for flare-induced disk heating.

[142] arXiv:1807.08521v1 [pdf, vox]

Kinematics of Spiral galaxies as a Portal to the Nature of Dark Matter

Paolo Salucci
Submitted Monday 23 July 2018 @ 10:43:14 GMT
Invited Talk. 8 pages 6 figs. To appear in "Particle Physics at the Year of 25th Anniversary of Lomonosov Conferences" (Proceedings of the 18th Lomonosov Conference on Elementary Particle Physics, Moscow, 24-30 August 2017), edited by Alexander Studenikin, World Scientific (Singapore), 2018

The gravitational field of Spiral galaxies is well traced by their rotation curves. Only recently it has become of extreme interest that the latter form a family ruled by two parameters of the {\it luminous} component: the disk length-scale $R_D$ and the magnitude $M_I$. This evidence is so strong and consequential that it must be taken as the starting point for the investigation on the issue of the dark matter in galaxies. The emerging fact is that structural quantities deeply rooted in the luminous components, like the disk length scales are found to tightly correlate with structural quantities deeply rooted in the dark component, like the DM halo core radii. This unexpected evidence may strongly call for a shift of paradigm with respect to the current Cold collisionless Dark Matter one.

[143] arXiv:1807.08516v1 [pdf, vox]

Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector

XMASS Collaboration, K. Abe, K. Hiraide, K. Ichimura, Y. Kishimoto, K. Kobayashi, M. Kobayashi, S. Moriyama, M. Nakahata, H. Ogawa, K. Sato, H. Sekiya, T. Suzuki, O. Takachio, A. Takeda, S. Tasaka, M. Yamashita, B. S. Yang, N. Y. Kim, Y. D. Kim, Y. Itow, K. Kanzawa, K. Masuda, K. Martens, Y. Suzuki, B. D. Xu, K. Miuchi, N. Oka, Y. Takeuchi, Y. H. Kim, K. B. Lee, M. K. Lee, Y. Fukuda, M. Miyasaka, K. Nishijima, K. Fushimi, G. Kanzaki, S. Nakamura
Submitted Monday 23 July 2018 @ 10:27:40 GMT
18 pages, 5 figures

Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the $\alpha' / \alpha$ parameter related to kinetic mixing of hidden photons and the coupling constant $g_{Ae}$ of axion-like particles in the mass range from 40 to 120 keV/$c^2$, resulting in $\alpha' / \alpha < 6 \times 10^{-26}$ and $g_{Ae} < 4 \times 10^{-13}$. These limits are the most stringent derived from both direct and indirect searches to date.

[144] arXiv:1807.08499v1 [pdf, vox]

Primordial Gas Collapse in The Presence of Radiation: Direct Collapse Black Hole or Population III star?

Bhaskar Agarwal
Submitted Monday 23 July 2018 @ 09:20:57 GMT
Preprint~of~a~review volume chapter to be published in Latif, M., \& Schleicher, D.R.G., "Primordial Gas Collapse in The Presence of Radiation: Direct Collapse Black Hole or Population III star?", Formation of the First Black Holes, 2018 \textcopyright Copyright World Scientific Publishing Company, https://www.worldsci​entific.com/worldsci​books/10.1142/10652

The first billion years in the evolution of the Universe mark the formation of the first stars, black holes and galaxies. The radiation from the first galaxies plays an important role in determining the final state of primordial gas collapsing in a neighboring halo. This is due to the fact that the primary coolant for primordial gas is molecular hydrogen, which can be dissociated into atomic hydrogen by Lyman-Werner photons in the energy range $11.2 - 13.6$~eV. While cooling by molecular hydrogen leads to Pop. III star formation, cooling by atomic hydrogen can lead to the formation of a supermassive star (or quasi-star) which results in the formation of a massive $10^{4-5} M_\odot$ black hole, or a direct collapse black hole. The spectrum of this radiation field is critical in order to determine whether a primordial gas cloud forms a Pop. III star or a very massive black hole. We will in the following explore this scenario and discuss how the radiation spectrum influences the outcome of the collapse.

[145] arXiv:1807.05530v2 [pdf, vox]

Cross-correlations between scalar perturbations and magnetic fields in bouncing universes

Debika Chowdhury, L. Sriramkumar, Marc Kamionkowski
Submitted Monday 23 July 2018 @ 08:43:43 GMT
v1: 29 pages, 3 figures; v2: 29 pages, 3 figures, references added

Bouncing scenarios offer an alternative to the inflationary paradigm for the generation of perturbations in the early universe. Recently, there has been a surge in interest in examining the issue of primordial magnetogenesis in the context of bouncing universes. As in the case of inflation, the conformal invariance of the electromagnetic action needs to be broken in bouncing scenarios in order to generate primordial magnetic fields which correspond to observed strengths today. The non-minimal coupling, which typically depends on a scalar field that possibly drives the homogeneous background, leads to a cross-correlation at the level of the three-point function between the perturbation in the scalar field and the magnetic fields. This has been studied in some detail in the context of inflation and, specifically, it has been established that the three-point function satisfies the so-called consistency relation in the squeezed limit. In this work, we study the cross-correlation between the magnetic fields and the perturbation in an auxiliary scalar field in a certain class of bouncing scenarios. We consider couplings that lead to scale invariant spectra of the magnetic field and evaluate the corresponding cross-correlation between the magnetic field and the perturbation in the scalar field. We find that, when compared to de Sitter inflation, the dimensionless non-Gaussianity parameter that characterizes the amplitude of the cross-correlations proves to be considerably larger in bouncing scenarios. We also show that the aforementioned consistency condition governing the cross-correlation is violated in the bouncing models. We discuss the implications of our results.

[146] arXiv:1807.07477v2 [pdf, vox]

Enhancing the cross-correlations between magnetic fields and scalar perturbations through parity violation

Debika Chowdhury, L. Sriramkumar, Marc Kamionkowski
Submitted Monday 23 July 2018 @ 08:37:23 GMT
v1: 20 pages, 4 figures; v2: 20 pages, 4 figures, references added. arXiv admin note: text overlap with arXiv:1807.05530

One often resorts to a non-minimal coupling of the electromagnetic field in order to generate magnetic fields during inflation. The coupling is expected to depend on a scalar field, possibly the same as the one driving inflation. At the level of three-point functions, such a coupling leads to a non-trivial cross-correlation between the perturbation in the scalar field and the magnetic field. This cross-correlation has been evaluated analytically earlier for the case of non-helical electromagnetic fields. In this work, we numerically compute the cross-correlation for helical magnetic fields. Non-Gaussianities are often generated as modes leave the Hubble radius. The helical electromagnetic modes evolve strongly (when compared to the non-helical case) around Hubble exit and one type of polarization is strongly amplified immediately after Hubble exit. We find that helicity considerably boosts the amplitude of the dimensionless non-Gaussianity parameter that characterizes the amplitude and shape of the cross-correlation between the perturbations in the scalar field and the magnetic field. We discuss the implications of the enhancement in the non-Gaussianity parameter due to parity violation.

[147] arXiv:1807.07280v3 [pdf, vox]

Duty cycle of the radio galaxy B2 0258+35

M. Brienza, R. Morganti, M. Murgia, N. Vilchez, B. Adebahr, E. Carretti, R. Concu, F. Govoni, J. Harwood, H. Intema, F. Loi, A. Melis, R. Paladino, S. Poppi, A. Shulevski, V. Vacca, G. Valente
Submitted Monday 23 July 2018 @ 07:47:00 GMT
13 pages, 4 figures, 6 tables, A&A accepted

Radio loud Active Galactic Nuclei are episodic in nature, cycling through periods of activity and quiescence. In this work we investigate the duty cycle of the radio galaxy B2~0258+35, which was previously suggested to be a restarted radio galaxy based on its morphology. The radio source consists of a pair of kpc-scale jets embedded in two large-scale lobes (~240 kpc) with relaxed shape and very low surface brightness, which resemble remnants of a past AGN activity. We have combined new LOFAR data at 145 MHz and new SRT data at 6600 MHz with available WSRT data at 1400 MHz to investigate the spectral properties of the outer lobes and derive their age. Interestingly, the spectrum of both the outer Northern and Southern lobes is not ultra-steep as expected for an old ageing plasma with spectral index values equal to $\rm \alpha_{1400}^{145}=​0.48\pm0.11$ and $\rm \alpha_{6600}^{1400}​=0.69\pm0.20$ in the outer Northern lobe, and $\rm \alpha_{1400}^{145}=​0.73\pm0.07$ in the outer Southern lobe. Moreover, despite the wide frequency coverage available for the outer Northern lobe (145-6600~MHz), we do not identify a significant spectral curvature (SPC$\simeq$0.2$\pm0​.2$). While mechanisms such as in-situ particle reacceleration, mixing or compression can temporarily play a role in preventing the spectrum from steepening, in no case seem the outer lobes to be compatible with being very old remnants of past activity as previously suggested (with age $\gtrsim$ 80 Myr). We conclude that either the large-scale lobes are still fuelled by the nuclear engine or the jets have switched off no more than a few tens of Myr ago. Our study shows the importance of combining morphological and spectral properties to reliably classify the evolutionary stage of low surface brightness, diffuse emission that low frequency observations are revealing around a growing number of radio sources.

[148] arXiv:1807.08453v1 [pdf, vox]

Color Classification of Extrasolar Giant Planets: Prospects and Cautions

Natasha E. Batalha, Adam J. R. W. Smith, Nikole K. Lewis, Mark S. Marley, Jonathan J. Fortney, Bruce Macintosh
Submitted Monday 23 July 2018 @ 07:01:30 GMT
16 pages, 11 figures, accepted AJ

Atmospheric characterization of directly imaged planets has thus far been limited to ground-based observations of young, self-luminous, Jovian planets. Near-term space- and ground- based facilities like \emph{WFIRST} and ELTs will be able to directly image mature Jovian planets in reflected light, a critical step in support of future facilities that aim to directly image terrestrial planets in reflected light (e.g. HabEx, LUVOIR). These future facilities are considering the use of photometry to classify planets. Here, we investigate the intricacies of using colors to classify gas-giant planets by analyzing a grid of 9,120 theoretical reflected light spectra spread across different metallicities, pressure-temperature profiles, cloud properties, and phase angles. We determine how correlated these planet parameters are with the colors in the \emph{WFIRST} photometric bins and other photometric bins proposed in the literature. Then we outline under what conditions giant planet populations can be classified using several supervised multivariate classification algorithms. We find that giant planets imaged in reflected light can be classified by metallicity with an accuracy of $>$90\% if they are \emph{a prior} known to not have significant cloud coverage in the visible part of the atmosphere, and at least 3 filter observations are available. If the presence of clouds is not known \emph{a priori}, directly imaged planets can be more accurately classified by their cloud properties, as oppposed to metallicity or temperature. Furthermore, we are able to distinguish between cloudy and cloud-free populations with $>$90\% accuracy with 3 filter observations. Our statistical pipeline is available on GitHub and can be extended to optimize science yield of future mission concepts.

[149] arXiv:1807.08433v1 [pdf, vox]

Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations

Adam P. Showman, Xianyu Tan, Xi Zhang
Submitted Monday 23 July 2018 @ 05:52:49 GMT
17 pages, 10 figures, submitted to ApJ

Brown dwarfs and directly imaged giant planets exhibit significant evidence for active atmospheric circulation, which induces a large-scale patchiness in the cloud structure that evolves significantly over time, as evidenced by infrared light curves and Doppler maps. These observations raise critical questions about the fundamental nature of the circulation, its time variability, and the overall relationship to the circulation on Jupiter and Saturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east-west) jet streams at the cloud level; moreover, both planets exhibit long-term stratospheric oscillations involving perturbations of zonal wind and temperature that propagate downward over time on timescales of ~4 years (Jupiter) and ~15 years (Saturn). These oscillations, dubbed the Quasi Quadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO) on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO) on Earth, which is driven by upward propagation of equatorial waves from the troposphere. To investigate these issues, we here present global, three-dimensional, high-resolution numerical simulations of the flow in the stratified atmosphere--overlyin​g the convective interior--of brown dwarfs and Jupiter-like planets. The effect of interior convection is parameterized by inducing small-scale, randomly varying perturbations in the radiative-convective boundary at the base of the model. In the simulations, the convective perturbations generate atmospheric waves and turbulence that interact with the rotation to produce numerous zonal jets. Moreover, the equatorial stratosphere exhibits stacked eastward and westward jets that migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian QQO, and Saturnian SAO. This is the first demonstration of a QBO-like phenomenon in 3D numerical simulations of a giant planet.

[150] arXiv:1807.08422v1 [pdf, vox]

Black Hole Shadow as a Test of General Relativity: Quadratic Gravity

Dimitry Ayzenberg, Nicolas Yunes
Submitted Monday 23 July 2018 @ 03:51:18 GMT
21 pages, 5 figures. Submitted to CQG

Observations of the black hole shadow of supermassive black holes, such as Sagittarius A* at the center of our Milky Way galaxy, allow us to study the properties of black holes and the nature of strong-field gravity. According to the Kerr hypothesis, isolated, stationary, and axisymmetric astrophysical black holes are described by the Kerr metric. The Kerr hypothesis holds in General Relativity and in some modified gravity theories, but there are others in which it is violated. In principle, black hole shadow observations can be used to determine if the Kerr metric is the correct description for black holes, and in turn, they could be used to place constraints on modified gravity theories that do not admit the Kerr solution. We here investigate whether black hole shadow observations can constrain deviations from general relativity, focusing on two well-motivated modified quadratic gravity theories: Einstein-dilaton-Gau​ss-Bonnet gravity and dynamical Chern-Simons gravity. We show that current constraints on Einstein-dilaton-Gau​ss-Bonnet gravity are stronger than any that could be placed with black hole shadow observations of supermassive black holes. We also show that the same holds for dynamical Chern-Simons gravity through a systematic bias and a likelihood analysis when considering slowly-rotating supermassive black holes. However, observations of more rapidly-rotating black holes, with dimensionless spins $|\vec{J}|/M^{2}\sim​eq0.5$, could be used to better constrain dynamical Chern-Simons gravity.

[151] arXiv:1807.08420v1 [pdf, vox]

Large-Amplitude Blazar Polarization Angle Swing as a Signature of Magnetic Reconnection

Haocheng Zhang, Xiaocan Li, Fan Guo, Dimitrios Giannios
Submitted Monday 23 July 2018 @ 03:46:32 GMT
Accepted for Publication in The Astrophysical Journal Letters

Relativistic magnetic reconnection events can widely exist in magnetized plasmas in astrophysical systems. During this process, oppositely directed magnetic field lines reconnect and release magnetic energy, efficiently accelerating nonthermal particles. However, so far there is little clear observational signatures of relativistic magnetic reconnection events in astrophysical systems. Blazars are relativistic magnetized plasma outflows from supermassive black holes. Their multi-wavelength flares may be powered by relativistic magnetic reconnection. The highly variable radiation and polarization signatures are well covered by multi-wavelength observation campaigns, making them ideal targets to examine the magnetic reconnection model. Recent observations have found that several blazar flares are accompanied by optical polarization angle swings which may be of as large amplitude as $> 180^{\circ}$, challenging existing theoretical models. In this paper, we present integrated particle-in-cell (PIC) and polarized radiation transfer simulations of magnetic reconnection events. We find that plasmoid coalescences in the reconnection layer can give rise to highly variable light curves, low and fluctuating polarization degree, and rotating polarization angle. In particular, large-amplitude polarization angle swings, similar to those observed during blazar flares, can be a unique signature of relativistic magnetic reconnection events.

Submitted Sun, 22 Jul 2018

[152] arXiv:1807.07548v2 [pdf, vox]

The Maximum Angular-Diameter Distance in Cosmology

Fulvio Melia, Manoj K. Yennapureddy
Submitted Sunday 22 July 2018 @ 22:23:11 GMT
10 pages, 5 figures, 2 tables. Matches final, published version in MNRAS

Unlike other observational signatures in cosmology, the angular-diameter distance d_A(z) uniquely reaches a maximum (at z_max) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, we estimate and use z_max inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing d_A(z) using Gaussian processes, and (3) comparing the predictions of seven different cosmologies and showing that the measured value of z_max can effectively discriminate between them. We find that z_max=1.70 +\- 0.20---an important new probe of the Universe's geometry. The most strongly favoured model is R_h=ct, followed by Planck LCDM. Several others, including Milne, Einstein-de Sitter and Static tired light are strongly rejected. According to these results, the R_h=ct universe, which predicts z_max=1.718, has a ~92.8% probability of being the correct cosmology. For consistency, we also carry out model selection based on d_A(z) itself. This test confirms that R_h=ct and Planck LCDM are among the few models that account for angular-size data better than those that are disfavoured by z_max. The d_A(z) comparison, however, is less discerning than that with z_max, due to the additional free parameter, H_0. We find that H_0=63.4 +\- 1.2 km/s/Mpc for R_h=ct, and 69.9 +\- 1.5 km/s/Mpc for LCDM. Both are consistent with previously measured values in each model, though they differ from each other by over 4 sigma. In contrast, model selection based on z_max is independent of H_0.

[153] arXiv:1807.08363v1 [pdf, vox]

A Search for Pulsars in Steep Spectrum Radio Sources

Yogesh Maan, Cees Bassa, Joeri van Leeuwen, M. A. Krishnakumar, Bhal Chandra Joshi
Submitted Sunday 22 July 2018 @ 20:52:31 GMT
Accepted for publication in ApJ

We report on a time-domain search for pulsars in 44 steep spectrum radio sources originally identified from recent imaging surveys. The time-domain search was conducted at 327 MHz using the Ooty radio telescope, and utilized a semi-coherent dedispersion scheme retaining the sensitivity even for sub-millisecond periods up to reasonably high dispersion measures. No new pulsars were found. We discuss the nature of these steep spectrum sources and argue that majority of the sources in our sample should either be pulsars or a new category of Galactic sources. Several possibilities that could hinder detection of these sources as pulsars, including anomalously high scattering or alignment of the rotation and magnetic axes, are discussed in detail, and we suggest unconventional search methods to further probe these possibilities.

[154] arXiv:1807.08356v1 [pdf, vox]

Unravelling the complex structure of AGN-driven outflows III. The outflow size-luminosity relation

Daeun Kang, Jong-Hak Woo
Submitted Sunday 22 July 2018 @ 20:01:43 GMT
Accepted for publication in ApJ

Energetic gas outflows driven by active galactic nuclei (AGNs) are considered as one of the mechanisms, by which supermassive black holes affect their host galaxies. To probe the impact of AGN-driven outflows, it is essential to quantify the size of the region under the influence of outflows. In the third of a series of papers, we present the spatially-resolved kinematics of ionized gas for 3 additional type 2 AGNs based on the Gemini Multi-Object Spectrograph (GMOS) integral field spectroscopy. Along with the 6 AGNs presented in our previous works and the 14 AGNs with available GMOS IFU data, we construct a sample of 23 luminous type 2 AGNs at z < 0.2, and kinematically measure the size of ionized gas outflows by tracing the radial decrease of the velocity dispersion of the [O iii] {\lambda}5007 emission line. The kinematically-measur​ed outflow size ranges from 0.60 to ~7.45 kpc, depending on AGN luminosity. We find that the size of the photoionized region is larger than the kinematically-measur​ed outflow size, while the flux-weighted photoionization size is significantly smaller. Thus, using the photoionization size as a proxy for the outflow size will lead to overestimation or underestimation, and introduce a large uncertainty of the mass outflow rate and the energy output rate. We report the outflow size-luminosity relation with a slope of 0.28{\pm}0.03, which is shallower than the slope of the correlation between the photoionization size and luminosity.

[155] arXiv:1807.08355v1 [pdf, vox]

Comparison of the generalized centroid with Gaussian and quadratic peak localization methods

Shannon Campbell
Submitted Sunday 22 July 2018 @ 19:39:02 GMT
6 pages,6 figures

We examine a new method for peak localization, the centroid of the data raised to some power, which we call the generalized centroid. We derive the peak localization uncertainty for the generalized centroid and compare it with the Cramer-Rao lower bound for both Gaussian and quadratic fits (with Gaussian signal and noise). We find that the centroid of squares and the Gaussian fit yield the best results in both one and two dimensions. We perform similar analysis with a Lorentz-like signal and find that the centroid of cubes and the nonlinear least squares fit provide the best results. We support our derivations with simulations, and also show simulation results when the maximum function is used to initially estimate the peak location.

[156] arXiv:1807.08322v1 [pdf, vox]

Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update

C. de la Fuente Marcos, R. de la Fuente Marcos
Submitted Sunday 22 July 2018 @ 17:19:31 GMT
4 pages, 1 figure. Accepted for publication in Research Notes of the AAS

Apollo meteoroid 2018 LA has become only the third natural object ever to be discovered prior to causing a meteor airburst and just the second one to have its meteorites recovered (at Botswana's Central Kalahari Game Reserve). Here, we use the latest orbit determination of 2018 LA (solution date 18-July-2018) to search for minor bodies moving in paths comparable to that of 2018 LA using the D-criteria, which are metrics to study orbit similarity, and N-body simulations. Our results further confirm the existence of a dynamical grouping of asteroids that might be related to 2018 LA and show that the impactor could be a recent fragment spawned by a larger object, the 550-m wide, potentially hazardous asteroid (454100) 2013 BO73. Spectroscopic observations of 454100 during its next flyby with our planet (brightest at an apparent visual magnitude of 18.4 on 2018 mid-November) may confirm or deny a putative similar chemical composition to that of the recovered meteorites of 2018 LA.

[157] arXiv:1807.08313v1 [pdf, vox]

Electromagnetic self force in curved spacetime: New insights from the Janis-Newman algorithm

Matteo Broccoli, Adriano Viganò
Submitted Sunday 22 July 2018 @ 16:34:12 GMT
4 pages

We present an original approach to compute the electromagnetic self force acting on a static charge in Kerr spacetime. Our approach is based on an improved version of the Janis-Newman algorithm and extends its range of applicability. It leads to a closed expression which generalizes the existing one and, since it does not involve the electromagnetic potential, it simplifies the calculation of the self force.

[158] arXiv:1807.08301v1 [pdf, vox]

Period spacings in red giants IV: Toward a complete description of the mixed-mode pattern

B. Mosser, C. Gehan, K. Belkacem, R. Samadi, E. Michel, M-J. Goupil
Submitted Sunday 22 July 2018 @ 15:28:34 GMT
Proposed for acceptance in A&A

Oscillation modes with a mixed character, as observed in evolved low-mass stars, are highly sensitive to the physical properties of the innermost regions. Measuring their properties is therefore extremely important to probe the core, but requires some care, due to the complexity of the mixed-mode pattern. This work aims at providing a consistent description of the mixed-mode pattern of low-mass stars, based on the asymptotic expansion. We also aim at studying the variation of the gravity offset $\varepsilon_{g}$ with stellar evolution. We revisit previous work about mixed modes in red giants and empirically test how period spacings, rotational splittings, mixed-mode widths and heights can be estimated in a consistent view, based on the properties of the mode inertia ratios. From the asymptotic fit of the mixed-mode pattern of a large set of red giants at various evolutionary stages, we derive unbiased and precise asymptotic parameters. As the asymptotic expansion of gravity modes is verified with a precision close to the frequency resolution for stars on the red giant branch (10$^{-4}$ in relative values), we can derive accurate values of the asymptotic parameters. We decipher the complex pattern in a rapidly rotating star, and explain how asymmetrical splittings can be inferred, as well as the stellar inclinations. This allows us to revisit the stellar inclinations in two open clusters, NGC 6819 and NGC 6791: our results show that the stellar inclinations in these clusters do not have privileged orientation in the sky. The variation of the asymptotic gravity offset along with stellar evolution is investigated in detail. We also derive generic properties that explain under which conditions mixed modes can be observed.

[159] arXiv:1807.08270v1 [pdf, vox]

Generalized Birkhoff theorem and its applications in mimetic gravity

Xin-zhou Li, Xiang-hua Zhai, Ping Li
Submitted Sunday 22 July 2018 @ 10:55:40 GMT
11 pages

There is undetermined potential function $V(\phi)$ in the action of mimetic gravity which should be resolved through physical means. In general relativity(GR), the static spherically symmetric(SSS) solution to the Einstein equation is a benchmark and its deformation also plays a crucial role in mimetic gravity. The equation of motion is provided with high nonlinearity, but we can reduce primal nonlinearity to a frequent Riccati form in the SSS case of mimetic gravity. In other words, we obtain an expression of solution to the functional differential equation of motion with any potential function. Remarkably, we proved rigorously that there is a zero point of first order for the metric function $\beta(r)$ if another metric function $\alpha(r)$ possesses a pole of first order within mimetic gravity. The zero point theorem may be regarded as the generalization of Birkhoff theorem $\alpha\beta=1$ in GR. As a corollary, we show that there is a modified black hole solution for any given $V(\phi)$, which can pass the test of solar system. As another corollary, the zero point theorem provides a dynamical mechanism for the maximum size of galaxies. Especially, there are two analytic solutions which provide good fits to the rotation curves of galaxies without the demand for particle dark matter.

[160] arXiv:1807.08258v1 [pdf, vox]

Stellar parameters of the two binary systems: HIP 14075 and HIP 14230

Suhail G. Masda, Mashhoor A. Al-Wardat, J. M. Pathan
Submitted Sunday 22 July 2018 @ 08:29:05 GMT
10 pages, 6 Figures and 4 Tables

We present the stellar parameters of the individual components of the two old close binary systems HIP\,14075 and HIP\,14230 using synthetic photometric analysis. These parameters are accurately calculated based on the best match between the synthetic photometric results within three different photometric systems with the observed photometry of the entire system. From the synthetic photometry, we derive the masses and radii of HIP\,14075 as: $\mathcal{M}^A=0.99\​pm0.19\, \mathcal{M_\odot}$, $R_{A}=0.877\pm0.08\​, R_\odot$ for the primary and $\mathcal{M}^B=0.96\​pm0.15\, \mathcal{M_\odot}$, $R_{B}=0.821\pm0.07\​, R_\odot$ for the secondary, and of HIP\,14230 as: $\mathcal{M}^A=1.18\​pm0.22\, \mathcal{M_\odot}$, $R_{A}=1.234\pm0.05\​, R_\odot$ for the primary and $\mathcal{M}^B=0.84\​pm0.12\, \mathcal{M_\odot}$, $R_{B}=0.820\pm0.05\​, R_\odot$ for the secondary, both systems depend on Gaia parallaxes. Based on the positions of the components of the two systems on a theoretical Hertzsprung- Russell diagram, we find that the age of HIP 14075 is $11.5\pm2.0$\,Gyr and of HIP 14230 is $3.5\pm1.5$\,Gyr. Our analysis reveals that both systems are old close binary systems ($\approx >$ 4 Gyr). Finally, the positions of the components of both systems on the stellar evolutionary tracks and isochrones are discussed.

[161] arXiv:1807.08251v1 [pdf, vox]

Ring Galaxies in the EAGLE Hydrodynamical Simulations

Ahmed Elagali, Claudia D. P. Lagos, O. Ivy Wong, Lister Staveley-Smith, James W. Trayford, Matthieu Schaller, Tiantian Yuan, Mario G. Abadi
Submitted Sunday 22 July 2018 @ 07:16:52 GMT
Submitted to MNRAS

We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations. We use the largest reference model Ref-L100N1504, a cubic cosmological volume of 100 comoving megaparsecs on a side, to identify and characterise these systems through cosmic time. The number density of ring galaxies in EAGLE is in broad agreement with the observations. The vast majority of ring galaxies identified in EAGLE (83 per cent) have an interaction origin, i.e., form when one or more companion galaxies drop-through a disk galaxy. The remainder (17 per cent) have very long-lived ring morphologies (> 2 Gyr) and host strong bars. Ring galaxies are HI rich galaxies, yet display inefficient star formation activity and tend to reside in the green valley particularly at z > 0.5. This inefficiency is mainly due to the low pressure and metallicity of their interstellar medium (ISM) compared with the ISM of similar star-forming galaxies. We find that the interaction(s) is responsible for decreasing the ISM pressure by causing the ISM gas to flow from the inner regions to the outer disk, where the ring feature forms. At a fixed radius, the star formation efficiency of ring galaxies is indistinguishable from their star-forming counterparts, and thus the main reason for their integrated lower efficiency is the different gas surface density profiles. Since galaxy morphologies are not used to tune the parameters in hydrodynamical simulations, the experiment performed here demonstrates the success of the current numerical models in EAGLE.

[162] arXiv:1807.08249v1 [pdf, vox]

Cosmological parameters from weak cosmological lensing

Martin Kilbinger
Submitted Sunday 22 July 2018 @ 06:48:06 GMT
Manuscript of the habilitation \`a diriger des recherches, required for supervising students in the French university system. 61 pages, text in English. Substantial overlap with arXiv:1411.0115

In this manuscript of the habilitation \`a diriger des recherches (HDR), the author presents some of his work over the last ten years. The main topic of this thesis is cosmic shear, the distortion of images of distant galaxies due to weak gravitational lensing by the large-scale structure in the Universe. Cosmic shear has become a powerful probe into the nature of dark matter and the origin of the current accelerated expansion of the Universe. Over the last years, cosmic shear has evolved into a reliable and robust cosmological probe, providing measurements of the expansion history of the Universe and the growth of its structure. I review the principles of weak gravitational lensing and show how cosmic shear is interpreted in a cosmological context. Then I give an overview of weak-lensing measurements, and present observational results from the Canada-France Hawai'i Lensing Survey (CFHTLenS), as well as the implications for cosmology. I conclude with an outlook on the various future surveys and missions, for which cosmic shear is one of the main science drivers, and discuss promising new weak cosmological lensing techniques for future observations.

[163] arXiv:1807.08231v1 [pdf, vox]

Computational Challenges and Opportunities of Simulating Cosmic Ray Showers at Global Scale

Olesya Sarajlic, Semir Sarajlic, Ting-Cun Wei, Xiaochun He
Submitted Sunday 22 July 2018 @ 03:26:48 GMT

Galactic cosmic rays are the high-energy particles that stream into our solar system from distant corners of our Galaxy and some low energy particles are from the Sun which are associated with solar flares. The Earth atmosphere serves as an ideal detector for the high energy cosmic rays which interact with the air molecule nuclei causing propagation of extensive air showers. In recent years, there are growing interests in the applications of the cosmic ray measurements which range from the space/earth weather monitoring, homeland security based on the cosmic ray muon tomography, radiation effects on health via air travel, etc. A simulation program (based on the GEANT4 software package developed at CERN) has been developed at Georgia State University for studying the cosmic ray showers in atmosphere. The results of this simulation study will provide unprecedented knowledge of the geo-position-depende​nt cosmic ray shower profiles and significantly enhance the applicability of the cosmic ray applications. In the paper, we present the computational challenges and the opportunities for carrying out the cosmic ray shower simulations at the global scale using various computing resources including XSEDE.

[164] arXiv:1807.08215v1 [pdf, vox]

Icy Grains from the Nucleus of Comet C/2013 US10 (Catalina)

Silvia Protopapa, Michael S. P. Kelley, Bin Yang, James M. Bauer, Ludmilla Kolokolova, Charles E. Woodward, Jacqueline V. Keane, Jessica M. Sunshine
Submitted Sunday 22 July 2018 @ 00:39:03 GMT
Accepted for publication in ApJ Letters, 12 pages, 4 figures

We present IRTF/SpeX and NEOWISE observations of the dynamically new comet C/2013 US$_{10}$ (Catalina), hereafter US10, from 5.8 au inbound, to near perihelion at 1.3 au, and back to 5.0 au outbound. We detect water ice in the coma of US10, assess and monitor the physical properties of the ice as insolation varies with heliocentric distance, and investigate the relationship between water ice and CO$_{2}$. This set of measurements is unique in orbital coverage and can be used to infer the physical evolution of the ice and, potentially, the nucleus composition. We report (1) nearly identical near-infrared spectroscopic measurements of the coma at $-$5.8 au, $-$5.0 au, +3.9 au (where $<$0 au indicates pre-perihelion epochs), all presenting evidence of water-ice grains, (2) a dust-dominated coma at 1.3 au and 2.3 au and, (3) an increasing CO$_{2}$/$Af\rho$ ratio from $-$4.9 au to 1.8 au. We propose that sublimation of the hyper-volatile CO$_{2}$ is responsible for dragging water-ice grains into the coma throughout the orbit. Once in the coma, the observability of the water-ice grains is controlled by the ice grain sublimation lifetime, which seems to require some small dust contaminant (i.e., non-pure ice grains). At |R$_{h}$|>=3.9 au, the ice grains are long-lived and may be unchanged since leaving the comet nucleus. We find the nucleus of comet US10 is made of, among other components, $\sim$1-micron water-ice grains containing up to 1% refractory materials.

Submitted Sat, 21 Jul 2018

[165] arXiv:1807.08210v1 [pdf, vox]

Prospects for the characterisation of exo-zodiacal dust with the VLTI

S. Ertel, O. Absil, D. Defrère, J. -C. Augereau, B. Mennesson
Submitted Saturday 21 July 2018 @ 23:34:15 GMT
Accepted for publication in Experimental Astronomy

Exo-zodiacal dust, exozodi for short, is warm (~300K) or hot (up to ~2000K) dust found in the inner regions of planetary systems around main sequence stars. In analogy to our own zodiacal dust, it may be located in or near the habitable zone or closer in, down to the dust sublimation distance. The study of the properties, distribution, and evolution of exozodis can inform about the architecture and dynamics of the innermost regions of planetary systems, close to their habitable zones. On the other hand, the presence of large amounts of exo-zodiacal dust may be an obstacle for future space missions aiming to image Earth-like exoplanets. The dust can be the most luminous component of extrasolar planetary systems, but predominantly emits in the near- to mid-infrared where it is outshone by the host star. Interferometry provides a unique method of separating the dusty from the stellar emission. We discuss the prospects of exozodi observations with the next generation VLTI instruments and summarize critical instrument specifications.

[166] arXiv:1807.08209v1 [pdf, vox]

The HOSTS Survey for Exozodiacal Dust: Preliminary results and future prospects

S. Ertel, G. M. Kennedy, D. Defrère, P. Hinz, A. B. Shannon, B. Mennesson, W. C. Danchi, C. Gelino, J. M. Hill, W. F. Hoffmann, G. Rieke, E. Spalding, J. M. Stone, A. Vaz, A. J. Weinberger, P. Willems, O. Absil, P. Arbo, V. P. Bailey, C. Beichman, G. Bryden, E. C. Downey, O. Durney, S. Esposito, A. Gaspar, P. Grenz, C. A. Haniff, J. M. Leisenring, L. Marion, T. J. McMahon, R. Millan-Gabet, M. Montoya, K. M. Morzinski, E. Pinna, J. Power, A. Puglisi, A. Roberge, E. Serabyn, A. J. Skemer, K. Stapelfeldt, K. Y. L. Su, V. Vaitheeswaran, M. C. Wyatt
Submitted Saturday 21 July 2018 @ 23:34:08 GMT
To appear in SPIE Astronomical Telescopes + Instrumentation 2018 proceedings

[abridged] The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed an N band nulling interferometric survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of our data have been analyzed and we present here an update of our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71% [+11%/-20%] for stars with previously detected mid- to far-infrared excess to 11% [+9%/-4%] for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.

[167] arXiv:1807.07074v2 [pdf, vox]

The Molecular and Ionized Gas Phases of an AGN-driven Outflow in a Typical Massive Galaxy at z=2

R. Herrera-Camus, L. J. Tacconi, R. Genzel, N. M. Foerster Schreiber, D. Lutz, A. D. Bolatto, S. Wuyts, A. Renzini, S. J. Lilly, S. Belli, H. Uebler, T. Shimizu, R. Davies, E. Sturm, F. Combes, J. Freundlich, S. Garcia-Burillo, P. Cox, A. Burkert, T. Naab, L. Colina, A. Saintonge, M. Cooper, C. Feruglio, A. Weiss
Submitted Saturday 21 July 2018 @ 22:13:56 GMT
20 pages, 14 figures. Submitted to ApJ

Nuclear outflows driven by accreting massive black holes are one of the main feedback mechanisms invoked at high-z to reproduce the distinct separation between star-forming, disk galaxies and quiescent spheroidal systems. Yet, our knowledge of feedback at high-z remains limited by the lack of observations of the multiple gas phases in galaxy outflows. In this work we use new deep, high-spatial resolution ALMA CO(3-2) and archival VLT/SINFONI H$\alpha$ observations to study the molecular and ionized components of the AGN-driven outflow in zC400528 ---a massive, main sequence galaxy at z=2.3 in the process of quenching. We detect a powerful molecular outflow that shows a positive velocity gradient and extends for at least ~10 kpc from the nuclear region, about three times the projected size of the ionized wind. The molecular gas in the outflow does not reach velocities high enough to escape the galaxy and is therefore expected to be reaccreted. Keeping in mind the various assumptions involved in the analysis, we find that the mass and energetics of the outflow are dominated by the molecular phase. The AGN-driven outflow in zC400528 is powerful enough to deplete the molecular gas reservoir on a timescale at least twice shorter than that needed to exhaust it by star formation. This suggests that the nuclear outflow is one of the main quenching engines at work in the observed suppression of the central star-formation activity in zC400528.

[168] arXiv:1807.08198v1 [pdf, vox]

The dearth of difference between central and satellite galaxies II. Comparison of observations with L-GALAXIES and EAGLE in star formation quenching

Enci Wang, Huiyuan Wang, Houjun Mo, Frank C. van den Bosch, S. H. Lim, Lixin Wang, Xiaohu Yang, Sihan Chen
Submitted Saturday 21 July 2018 @ 19:55:05 GMT
19 pages, 12 figures; accepted for publication in ApJ

As we demonstrated in Paper I, the quenched fractions of central and satellite galaxies as function of halo mass are extremely similar, as long as one controls for stellar mass. The same holds for the quenched fractions as a function of central velocity dispersion, which is tightly correlated with black hole mass, as long as one controls for both stellar and halo mass. Here we use mock galaxy catalogs constructed from the latest semi-analytic model, L-GALAXIES, and the state-of-the-art hydrodynamical simulation, EAGLE, to investigate whether these models can reproduce the trends seen in the data. We also check how the group finder used to identify centrals and satellites impacts our results. We find that L-GALAXIES fails to reproduce the trends. The predicted quenched fraction of central galaxies increases sharply with halo mass around $10^{12.5}h^{-1}M_{\​odot}$ and with black hole mass around $\sim10^{6.5}M_{\odo​t}$, while the predicted quenched fraction of satellites increases with both halo and black hole masses gradually. In contrast, centrals and satellites in EAGLE follow almost the same trend as seen in the data. We discuss the implications of our results for how feedback processes regulate galaxy quenching.

[169] arXiv:1807.08174v1 [pdf, vox]

The AMY (Air Microwave Yield) experiment to measure the GHz emission from air shower plasma

J. Alvarez-Muniz, M. Blanco, M. Bohacova, B. Buonomo, G. Cataldi, M. R. Coluccia, P. Creti, I. De Mitri, C. Di Giulio, P. Facal San Luis, L. Foggetta, R. Gaior, D. Garcia-Fernandez, M. Iarlori, S. Le Coz, A. Letessier-Selvon, K. Louedec, I. C. Maris, D. Martello, G. Mazzitelli, L. Perrone, S. Petrera, V. Rizi, G. Rodriguez Fernandez, F. Salamida, G. Salina, M. Settimo, P. Valente, J. R. Vazquez, V. Verzi, C. Williams
Submitted Saturday 21 July 2018 @ 16:40:16 GMT
Proceedings of 6th International Conference on Acoustic and Radio EeV Neutrino Detection Activities, Annapolis (Maryland), USA, 2014

The aim of the Air Microwave Yield (AMY) experiment is to investigate the Molecular Bremsstrahlung Radiation (MBR) emitted from an electron beam induced air-shower. The measurements have been performed with a 510 MeV electron beam at the Beam Test Facility (BTF) of Frascati INFN National Laboratories in a wide frequency range between 1 and 20 GHz. We present the experimental apparatus and the first results of the measurements. Contrary to what have been reported in a previous similar experiment~\cite{Gor​ham-SLAC}, we have found that the intensity of the emission is strongly influenced by the particular time structure of the accelerator beam. This makes very difficult the interpretation of the emission process and a realistic extrapolation of the emission yield to the plasma generated during the development of an atmospheric shower.

[170] arXiv:1807.08161v1 [pdf, vox]

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating

E. R. Priest, L. P. Chitta, P. Syntelis
Submitted Saturday 21 July 2018 @ 14:13:13 GMT
8 pages, 4 figures

Nanoflare models for heating the solar corona usually assume magnetic braiding and reconnection as the source of the energy. However, recent observations at record spatial resolution from the {\sc Sunrise} balloon mission suggest that photospheric magnetic flux cancellation is much more common than previously realised. We therefore examine the possibility of three-dimensional reconnection driven by flux cancellation as a cause of chromospheric and coronal heating. In particular, we estimate how the heights and amount of energy release produced by flux cancellation depend on flux size, flux cancellation speed and overlying field strength.

[171] arXiv:1807.08153v1 [pdf, vox]

Dynamical Evidence of a Solitonic Core of $10^{9}M_\odot$ in the Milky Way

Ivan De Martino, Tom Broadhurst, S. -H. Henry Tye, Tzihong Chiueh, Hsi-Yu Schive
Submitted Saturday 21 July 2018 @ 13:42:59 GMT
5 pages, 2 figures

A wavelike solution for the non-relativistic universal dark matter (wave-DM) is rapidly gaining interest, following distinctive predictions of pioneering simulations of cosmic structure as an interference pattern of coherently oscillating bosons. A prominent solitonic standing wave is predicted at the center of every galaxy, representing the ground state, that has been identified with the wide, kpc scale dark cores of common dwarf-spheroidal galaxies, providing a boson mass of, $\simeq 10^{-22}$ eV. A denser soliton is predicted for Milky Way sized galaxies where momentum is higher, so the de Broglie scale of the soliton is smaller, $\simeq 100pc$, of mass $\simeq 10^9 M_\odot$. Here we show the central motion of bulge stars in the Milky Way implies the presence of such a dark core, where the velocity dispersion rises inversely with radius to a maximum of $\simeq 130km/s$, corresponding to an excess central mass of $\simeq 1.5\times 10^9M_\odot$ within $\simeq 100$ pc, favouring a boson mass of $\simeq 10^{-22}$ eV. This quantitative agreement with such a unique and distinctive prediction is therefore strong evidence for a light bosonic solution to the long standing Dark Matter puzzle, such as the axions generic in String Theory.

[172] arXiv:1807.08121v1 [pdf, vox]

Low resolution spectroscopic investigation of Am stars using Automated method

Kaushal Sharma, Santosh Joshi, H. P. Singh
Submitted Saturday 21 July 2018 @ 10:11:28 GMT
4 pages, 2 figures, Proceeding for "First Belgo-Indian Network for Astronomy & Astrophysics (BINA) workshop", held in Nainital (India), November 15-18, 2016. Published in Bulletin of Li\`ege Royal Society of Sciences Vol. 87, p. 121-124

Automated method of full spectrum fitting gives reliable estimates of stellar atmospheric parameters (Teff, logg and [Fe/H]) for late A, F, G and early K type stars. Recently, the technique was further improved in the cooler regime and the validity range was extended up to M6 - M7 spectral type( Teff $\sim\,2900$ K). The present study aims to explore the application of this method on the low-resolution spectra of Am stars, a class of chemically peculiar (CP) stars, to examine its robustness for these objects. We use ULySS with MILES (Medium-resolution INT Library of Empirical Spectra) V2 spectral interpolator for parameter determination. Determined Teff and logg are found to be in good agreement with those obtained from high-resolution spectroscopy.

[173] arXiv:1807.08116v1 [pdf, vox]

Smoothed-Particle Hydrodynamics Models: Implementation Features on GPUs

Sergey Khrapov, Alexander Khoperskov
Submitted Saturday 21 July 2018 @ 10:01:07 GMT
12 pages, 5 figures. arXiv admin note: text overlap with arXiv:0810.3579 by other authors

Parallel implementation features of self-gravitating gas dynamics modeling on multiple GPUs are considered applying the GPU-Direct technology. The parallel algorithm for solving of the self-gravitating gas dynamics problem based on hybrid OpenMP-CUDA parallel programming model has been described in detail. The gas-dynamic forces are calculated by the modified SPH-method (Smoothed Particle Hydrodynamics) while the N-body problem gravitational interaction is obtained by the direct method (so-called Particle-Particle algorithm). The key factor in the SPH-method performance is creation of the neighbor lists of the particles which contribute into the gas-dynamic forces calculation. Our implementation is based on hierarchical grid sorting method using a cascading algorithm for parallel computations of partial sums at CUDA block. The parallelization efficiency of the algorithm for various GPUs of the Nvidia Tesla line (K20, K40, K80) is studied in the framework of galactic' gaseous halos collisions models by the SPH-method.

[174] arXiv:1807.08115v1 [pdf, vox]

Study on the mapping of halo clustering from real space to redshift space

Yi Zheng, Yong-Seon Song, Minji Oh
Submitted Saturday 21 July 2018 @ 09:58:04 GMT
28 pages, 9 figures

The mapping of galaxy clustering from real space to redshift space introduces the anisotropic property to the measured galaxy density power spectrum in redshift space, known as the redshift space distortion (RSD) effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to indefinite orders of cross correlations between density and velocity fields, and the Finger--of--God (FoG) effect due to the randomness of the galaxy peculiar velocity field. In previous works, we have verified the robustness of advanced TNS mapping formula in our hybrid RSD model in dark matter case, where the halo bias models are not taken into account for the halo mapping formula in redshift space. Using 100 realizations of halo catalogs in N-body simulations, we find that our halo RSD model with the known halo bias model and the effective FoG function accurately predicts the halo power spectrum measurements, within 1$\sim$2% accuracy up to $k\sim 0.2h$/Mpc, depending on different halo masses and redshifts.

[175] arXiv:1807.08113v1 [pdf, vox]

Estimating Stellar Atmospheric Parameters by Automated Methods Using SSLs

Kaushal Sharma, H. P. Singh, A. Kashyap, P. Prugniel
Submitted Saturday 21 July 2018 @ 09:39:32 GMT
4 pages, 2 figures, Proceeding for the "International Workshop on Spectral Stellar Libraries, 2017 (IWSSL2017)" held in Sao Paulo, Brazil, February 6-10, 2017. ASI Conference Series, 2017, Vol. 14. Edited by P. Coelho, L. Martins & E. Griffin, pp. 69-72, published

Libraries of stellar spectra, such as ELODIE (Prugniel & Soubiran 2001), CFLIB (Valdes et al. 2004), or MILES (S\'anchez-Bl\'azque​z et al. 2006), are used for a variety of applications, and especially in modelling stellar populations (e. g. Le Borgne et al. (2004)). In that context, apart from the completeness and quality of these spectral databases (Singh et al. 2006), the accurate calibration of stellar atmospheric parameters, temperature (Teff), surface gravity (log g), and metallicity ([Fe/H]), is known to be critical (Prugniel et al. 2007; Percival & Salaris 2009). We discuss the technique of determining stellar atmospheric parameters accurately by `full spectrum fitting'.

[176] arXiv:1807.08103v1 [pdf, vox]

The effect of magnetic field morphology on the structure of massive IRDC clumps

Nahid Bahmani, Mohsen Nejad-Asghar
Submitted Saturday 21 July 2018 @ 07:58:20 GMT
accepted by Ap&SS

Infrared dark clouds (IRDCs) have dense elongated clumps and filaments with the favorable viewing condition of being on the near-side of a bright mid-infrared background. The clumps usually have multiple cores around the center. In this work, we study the effect of magnetic field morphology on the structure of massive IRDC clumps. To achieve this goal, we consider an axisymmetric isothermal oblate IRDC clump, embedded into a constant external magnetic field. We assume a polynomial function for the magnetic field morphology inside the clump. We use the numerical iterative methods to solve the equations: the successive over-relaxation method to find the magnetic and gravitational fluxes, and then the bicongugate gradient method to find the optimized values of mass and current densities. The results show that the IRDC clump will be very elongated along the perpendicular direction of the external magnetic field lines. Also, the assumption of choosing of a polynomial function for the magnetic field morphology leads to the formation of dense regions around the center. The greater the density of the central region, the larger the density of these dense regions and the closer to the center. The presence of these dense regions can lead to the formation of cores at these points.

Submitted Fri, 20 Jul 2018

[177] arXiv:1807.08049v1 [pdf, vox]

Angular Momentum Loss for a Binary System in Einstein-Æther Theory

Alexander Saffer, Nicolas Yunes
Submitted Friday 20 July 2018 @ 22:57:26 GMT
9 pages, 2 figures, submitted to PRD

The recent gravitational wave observations provide insight into the extreme gravity regime of coalescing binaries, where gravity is strong, dynamical and non-linear. The interpretation of these observations relies on the comparison of the data to a gravitational wave model, which in turn depends on the orbital evolution of the binary, and in particular on its orbital energy and angular momentum decay. In this paper, we calculate the latter in the inspiral of a non-spinning compact binary system within Einstein-\AE{}ther theory. From the theory's gravitational wave stress energy tensor and a balance law, we compute the angular momentum decay both as a function of the fields in the theory and as a function of the multipole moments of the binary. We then specialize to a Keplerian parameterization of the orbit to express the angular momentum decay as a function of the binary's orbital elements. We conclude by combining this with the orbital energy decay to find expressions for the decay of the semi-major axis and the orbital eccentricity of the binary. We find that these rates of decay are typically faster in Einstein-\AE{}ther theory than in General Relativity due to the presence of dipole radiation. Such modifications will imprint onto the chirp rate of gravitational waves, leaving a signature of Einstein-\AE{}ther theory that if absent in the data could be used to stringently constrain it.

[178] arXiv:1807.08044v1 [pdf, vox]

Transforming the Canada France Hawaii Telescope (CFHT) into the Maunakea Spectroscopic Explorer (MSE): A Conceptual Observatory Building and Facilities Design

Steven E. Bauman, Greg Barrick, Tom Benedict, Armando Bilbao, Alexis Hill, Nicolas Flagey, Casey Elizares, Mike Gedig, Greg Green, Eric Grigel, David Lo, Ivan Look, Thomas Lorentz, Nathan Loewen, Eric Manuel, Alan McConnachie, Ronny Muller, Gaizka Murga, Rick Murowinski, Federico Ruan, Derrick Salmon, Kei Szeto, Jose Teran, Rafael Urrutia
Submitted Friday 20 July 2018 @ 22:14:08 GMT
23 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Observatory Operations: Strategies, Processes, and Systems VII

The Canada France Hawaii Telescope Corporation (CFHT) plans to repurpose its observatory on the summit of Maunakea and operate a new wide field spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). MSE will upgrade the observatory with a larger 11.25m aperture telescope and equip it with dedicated instrumentation to capitalize on the site, which has some of the best seeing in the northern hemisphere, and offer its user community the ability to do transformative science. The knowledge and experience of the current CFHT staff will contribute greatly to the engineering of this new facility. MSE will reuse the same building and telescope pier as CFHT. However, it will be necessary to upgrade the support pier to accommodate a bigger telescope and replace the current dome since a wider slit opening of 12.5 meters in diameter is needed. Once the project is completed the new facility will be almost indistinguishable on the outside from the current CFHT observatory. MSE will build upon CFHT's pioneering work in remote operations, with no staff at the observatory during the night, and use modern technologies to reduce daytime maintenance work. This paper describes the design approach for redeveloping the CFHT facility for MSE including the infrastructure and equipment considerations required to support and facilitate nighttime observations. The building will be designed so existing equipment and infrastructure can be reused wherever possible while meeting new requirement demands. Past experience and lessons learned will be used to create a modern, optimized, and logical layout of the facility. The purpose of this paper is to provide information to readers involved in the MSE project or organizations involved with the redevelopment of an existing observatory facility for a new mission.

[179] arXiv:1807.09180v1 [pdf, vox]

Maunakea Spectroscopic Explorer (MSE) - The Prime Focus Subsystems: Requirements and Interfaces

Alexis Hill, Alexandre Blin, David Horville, Shan Mignot, Kei Szeto
Submitted Friday 20 July 2018 @ 22:08:35 GMT
14 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Modeling, Systems Engineering, and Project Management for Astronomy VIII

MSE will be a massively multiplexed survey telescope, including a segmented primary mirror which feeds fibers at the prime focus, including an array of approximately four thousand fibers, positioned precisely to feed banks of spectrographs several tens of meters away. We describe the process of mapping top-level requirements on MSE to technical specifications for subsystems located at the MSE prime focus. This includes the overall top-level requirements based on knowledge of similar systems at other telescopes and how those requirements were converted into specifications so that the subsystems could begin working on their Conceptual Design Phases. We then discuss the verification of the engineering specifications and the compiling of lower-level requirements and specifications into higher level performance budgets (e.g. Image Quality). We also briefly discuss the interface specifications, their effect on the performance of the system and the plan to manage them going forward. We also discuss the opto-mechanical design of the telescope top end assembly and refer readers to more details for instrumentation located at the top end.

[180] arXiv:1807.09181v1 [pdf, vox]

Sphinx: a massively multiplexed fiber positioner for MSE

Scott Smedley, Gabriella Baker, Rebecca Brown, James Gilbert, Peter Gillingham, Will Saunders, Andrew Sheinis, Sudharshan Venkatesan, Lew Waller
Submitted Friday 20 July 2018 @ 22:05:15 GMT
18 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

In this paper we present the Australian Astronomical Observatory's concept design for Sphinx - a fiber positioned with 4332 spines on a 7.77mm pitch for CFHT's Mauna Kea Spectroscopic Explorer (MSE) Telescope. Based on the Echidna technology used with FMOS (on Subaru) and 4MOST (on VISTA), the next evolution of the tilting spine design delivers improved performance and superior allocation efficiency. Several prototypes have been constructed that demonstrate the suitability of the new design for MSE. Results of prototype testing are presented, along with an analysis of the impact of tilting spines on the overall survey efficiency. The Sphinx fiber positioned utilizes a novel metrology system for spine position feedback. The metrology design and the careful considerations required to achieve reliable, high accuracy measurements of all fibres in a realistic telescope environment are also presented.

[181] arXiv:1807.09182v1 [pdf, vox]

Automated testing of optical fibres: towards the design of the Maunakea Spectroscopic Explorer Fibre Transmission System

Stephanie Monty, Farbod Jahandar, Jooyoung Lee, Kim A. Venn, Colin Bradley, Darren Erickson, David Crampton, Victor Nicolov, Collin L. Kielty, Celine Mazoukh, Patrick Hall
Submitted Friday 20 July 2018 @ 21:54:23 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

We present the results of an automated fibre optic test bench constructed at the University of Victoria as part of the Maunakea Spectroscopic Explorer (MSE) Fibre Transmission System (FiTS). In preparation for MSE-FiTS, we have begun characterizing the focal ratio degradation (FRD) of candidate multi-mode fibres with the ultimate goal of testing all ~4000 MSE fibres. To achieve this, we have built an optical bench to perform an automated version of the collimated beam test. Herein we present the design of the bench and discuss the automation of components by introducing the Big FiTS Fibre Wrapper (Big FFW), our open-source automation software. We conclude with the results of tests performed using the Big FFW on a sample of candidate fibre, comparing the Big FFW results against those found using manual methods. Our results suggest that the candidate MSE fibre meets the science requirement of < 5% FRD at f=2 and less than 1% disagreement between both measurement methods.

[182] arXiv:1807.08041v1 [pdf, vox]

Radiative Signatures of Plasmoid-Dominated Reconnection in Blazar Jets

I. M. Christie, M. Petropoulou, L. Sironi, D. Giannios
Submitted Friday 20 July 2018 @ 21:48:07 GMT
19 pages, 14 figures

The multi-wavelength spectral and temporal variability observed in blazars set tight constraints on current theoretical emission models. Here, we investigate the relativistic magnetic reconnection process as a source of blazar emission in which quasi-spherical plasmoids, containing relativistic particles and magnetic fields, are associated with the emission sites in blazar jets. By coupling recent two-dimensional particle-in-cell simulations of relativistic reconnection with a time-dependent radiative transfer code, we compute the non-thermal emission from a chain of plasmoids formed during a reconnection event. The derived photon spectra display characteristic features observed in both BL Lac sources and flat spectrum radio quasars, with the distinction made by varying the strength of the external photon fields, the jet magnetization, and the number of pairs per proton contained within. Light curves produced from reconnection events are composed of many fast and powerful flares that appear on excess of a slower evolving envelope produced by the cumulative emission of medium-sized plasmoids. The observed variability is highly dependent upon the orientation of the reconnection layer with respect to the blazar jet axis and to the observer. Our model provides a physically motivated framework for explaining the multi-timescale blazar variability across the entire electromagnetic spectrum.

[183] arXiv:1807.08036v1 [pdf, vox]

MSE FiTS: the ultimate multi-fiber optic transmission system

Kim Venn, Darren Erickson, David Crampton, Rafal Pawluczyk, Paul Fournier, Pat Hall, Colin Bradley, Alan McConnachie, John Pazder, Farbod Jahandar, Stephanie Monty, Jooyoung Lee, Celine Mazoukh, Collin Kielty, Victor Nicolov, Kei Szeto, Alexis Hill
Submitted Friday 20 July 2018 @ 21:27:42 GMT
14 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

The Maunakea Spectroscopic Explorer (MSE) is a next-generation observatory, designed to provide highly multiplexed, multi-object spectroscopy over a wide field of view. The observatory will consist of (1) a telescope with an 11.25 m aperture, (2) a 1.5 square-degree science field of view, (3) fibre optic positioning and transmission systems, and (4) a suite of low (R=3000), moderate (R=6000) and high resolution (R=40,000) spectrographs. The Fibre Transmission System (FiTS) consists of 4332 optical fibres, designed to transmit the light from the telescope prime focus to the dedicated spectrographs. The ambitious science goals of MSE require the Fibre Transmission System to deliver performance well beyond the current state of the art for multi-fibre systems, e.g., the sensitivity to observe magnitude 24 objects over a very broad wavelength range (0.37 - 1.8 microns) while achieving relative spectrophotometric accuracy of <3% and radial velocity precision of 20 km/s.

[184] arXiv:1807.08035v1 [pdf, vox]

Modeling and budgeting fiber injection efficiency for the Maunakea spectroscopic explorer (MSE)

Nicolas Flagey, Kei Seto, Shan Mignon, Alexis Hill, Alan McConnachie, Calum Hervieu
Submitted Friday 20 July 2018 @ 21:19:32 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Modeling, Systems Engineering, and Project Management for Astronomy VIII

The Maunakea Spectroscopic Explorer (MSE) will each year obtain millions of spectra in the optical to near-infrared, at low (R ~ 3,000) to high (R ~ 40,000) spectral resolution by observing >4,000 spectra per pointing via a highly multiplexed fiber-fed system. Key science programs for MSE include black hole reverberation mapping, stellar population analysis of faint galaxies at high redshift, and sub-km/s velocity accuracy for stellar astrophysics. One key metric of the success of MSE will be its survey speed, i.e. how many spectra of good signal-to-noise ratio will MSE be able to obtain every night and every year. The survey speed is directly linked to the allocation efficiency - how many fibers in the focal surface can be allocated to targets - and to the injection efficiency - what fraction of light from a target can enter the fiber at the focal surface. In this paper we focus on the injection efficiency and how to optimize it to increase the signal-to-noise ratio of targets observed in sky dominated conditions. The injection efficiency depends on the size of the fiber and requires highly precise, repeatable and stable positioning of the fiber in the focal surface. We present the allocation budget used for Conceptual Design Review and the modeling that allows to estimate the injection efficiency, which is just one part necessary to meet the science requirements on sensitivities.

[185] arXiv:1807.08034v1 [pdf, vox]

Two novel approaches to the hadron-quark mixed phase in compact stars

Vahagn Abgaryan, David Alvarez-Castillo, Alexander Ayriyan, David Blaschke, Hovik Grigorian
Submitted Friday 20 July 2018 @ 21:18:56 GMT
15 pages, 9 figures

First-order phase transitions, like the liquid-gas transition, proceed via formation of structures such as bubbles and droplets. In strongly interacting compact star matter, at the crust-core transition, but also at the hadron-quark transition in the core, these structures form different shapes dubbed "pasta phases". We describe two methods to obtain one-parameter families of hybrid equations of state (EoS) which mimic the thermodynamic behavior of pasta phases in between a low-density hadron and a high-density quark matter phase, thus generalizing the Maxwell construction. The first method replaces the behavior of pressure vs. chemical potential in a finite region around the critical %chemical potential pressure of the Maxwell construction by a polynomial interpolation. The second method uses extrapolations of the hadronic and quark matter EoS beyond the Maxwell point to define a mixing of both with weight functions bounded by finite limits around the Maxwell point. We apply both methods to the case of a hybrid EoS with a strong first order transition that entails the formation of a third family of compact stars and the corresponding mass twin phenomenon. We investigate for both models the robustness of this phenomenon against variation of the single parameter, the pressure increment at the critical chemical potential which quantifies the deviation from the Maxwell construction. We also show sets of results for other compact star observables than mass and radius, namely the moment of inertia and the baryon mass.

[186] arXiv:1807.08033v1 [pdf, vox]

Expected observing efficiency of the Maunakea Spectroscopic Explorer (MSE)

Nicolas Flagey, Kei Seto, Kevin Ho, Billy Mahoney, Alan McConnachie, Alexis Hill, Calum Hervieu
Submitted Friday 20 July 2018 @ 21:14:44 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Observatory Operations: Strategies, Processes, and Systems VII

The Maunakea Spectroscopic Explorer (MSE) will obtain millions of spectra each year in the optical to near-infrared, at low (R ~ 3,000) to high (R ~ 40,000) spectral resolution by observing >4,000 spectra per pointing via a highly multiplexed fiber-fed system. Key science programs for MSE include black hole reverberation mapping, stellar population analysis of faint galaxies at high redshift, and sub-km/s velocity accuracy for stellar astrophysics. One key metric of the success of MSE will be its survey speed, i.e. how many spectra of good signal-to-noise ratio will MSE be able to obtain every night and every year. This is defined at the higher level by the observing efficiency of the observatory and should be at least 80%, as indicated in the Science Requirements. In this paper we present the observing efficiency budget developed for MSE based on historical data at the Canada-France-Hawaii Telescope and other Maunakea Observatories. We describe the typical sequence of events at night to help us compute the observing efficiency and how we envision to optimize it to meet the science requirements.

[187] arXiv:1807.08029v1 [pdf, vox]

The science calibration challenges of next generation highly multiplexed optical spectroscopy: the case of the Maunakea Spectroscopic Explorer

Alan W. McConnachie, Nicolas Flagey, Pat Hall, Will Saunders, Kei Szeto, Alexis Hill, Shan Mignot
Submitted Friday 20 July 2018 @ 21:09:44 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Observatory Operations: Strategies, Processes, and Systems VII

MSE is an 11.25m telescope with a 1.5 sq.deg. field of view. It can simultaneously obtain 3249 spectra at R=3000 from 360-1800nm, and 1083 spectra at R=40000 in the optical. The large field of view, large number of targets, as well as the use of more than 4000 optical fibres to transport the light from the focal plane to the spectrographs, means that precise and accurate science calibration is difficult but essential to obtaining the science goals. As a large aperture telescope focusing on the faint Universe, precision sky subtraction and spectrophotometry are especially important. Here, we discuss the science calibration requirements, and the adopted calibration strategy, including operational features and hardware, that will enable the successful scientific exploitation of the vast MSE dataset.

[188] arXiv:1807.08027v1 [pdf, vox]

Maunakea Spectroscopic Explorer (MSE): Implementing systems engineering methodology for the development of a new facility

Kei Szeto, Alexis Hill, Nicolas Flagey, Calum Hervieu, Mick Edgar, Peter Gillingham, Alan McConnachie, Shan Mignot, Richard Murowinski
Submitted Friday 20 July 2018 @ 20:55:06 GMT
20 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Modeling, Systems Engineering, and Project Management for Astronomy VIII

Maunakea Spectroscopic Explorer will be a 10-m class highly multiplexed survey telescope, including a segmented primary mirror and robotic fiber positioners at the prime focus. MSE will replace the Canada France Hawaii Telescope (CFHT) on the summit of Mauna Kea, Hawaii. The multiplexing includes an array of over four thousand fibres feeding banks of spectrographs several tens of meters away. We present an overview of the requirements flow-down for MSE, from Science Requirements Document to Observatory Requirements Document. We have developed the system performance budgets, along with updating the budget architecture of our evolving project. We have also identified the links between subsystems and system budgets (and subsequently science requirements) and included system budget that are unique to MSE as a fiber-fed facility. All of this has led to a set of Observatory Requirements that is fully consistent with the Science Requirements.

[189] arXiv:1807.08025v1 [pdf, vox]

Maximising the sensitivity of next generation multi-object spectroscopy: system budget development and design optimizations for the Maunakea Spectroscopic Explorer

Alan W. McConnachie, Nicolas Flagey, Kei Seto, Shan Mignon, Alexis Hill, Pat Hall
Submitted Friday 20 July 2018 @ 20:50:43 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Modeling, Systems Engineering, and Project Management for Astronomy VIII

MSE is an 11.25m telescope with a 1.5 sq.deg. field of view. It can simultaneously obtain 3249 spectra at R=3000 from 360-1800nm, and 1083 spectra at R=40000 in the optical. Absolutely critical to the scientific success of MSE is to efficiently access the faint Universe. Here, we describe the adopted systems engineering methodology to ensure MSE meets the challenging sensitivity requirements, and how these requirements are partitioned across three budgets, relating to the throughput, noise and fiber injection efficiency. We then describe how the sensitivity of MSE as a system was estimated at the end of Conceptual Design Phase, and how this information was used to revisit the system design in order to meet the sensitivity requirements while maintaining the overall architectural concept of the Observatory. Finally, we present the anticipated sensitivity performance of MSE and describe the key science that these capabilities will enable.

[190] arXiv:1807.08019v1 [pdf, vox]

Optimal scheduling and science delivery of spectra for millions of targets in thousands of fields: the operational concept of the Maunakea spectroscopic explorer (MSE)

Nicolas Flagey, Alan McConnachie, Kei Seto, Patrick Hall, Alexis Hill, Calum Hervieu
Submitted Friday 20 July 2018 @ 20:24:06 GMT
Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Observatory Operations: Strategies, Processes, and Systems VII

The Maunakea Spectroscopic Explorer (MSE) will each year obtain millions of spectra in the optical to near-infrared, at low (R~3000) to high (R~40000) spectral resolution by observing >3000 spectra per pointing via a highly multiplexed fiber-fed system. Key science programs for MSE include black hole reverberation mapping, stellar population analysis of faint galaxies at high redshift, and sub-km/s velocity accuracy for stellar astrophysics. The architecture of MSE is an assembly of subsystems designed to meet the science requirements and describes what MSE will look like. In this paper we focus on the operations concept of MSE, which describes how to operate a fiber fed, highly multiplexed, dedicated observatory given its architecture and the science requirements. The operations concept details the phases of operations, from selecting proposals within the science community to distributing back millions of spectra to this community. For each phase, the operations concept describes the tools required to support the science community in their analyses and the operations staff in their work. It also highlights the specific needs related to the complexity of MSE with millions of targets to observe, thousands of fibers to position, and different spectral resolution to use. Finally, the operations concept shows how the science requirements on calibration and observing efficiency can be met.

[191] arXiv:1807.08017v1 [pdf, vox]

Maunakea Spectroscopic Explorer (MSE) Instrumentation Suite

Alexis Hill, Nicolas Flagey, Alan McConnachie, Rick Murowinski, Kei Szeto
Submitted Friday 20 July 2018 @ 20:16:02 GMT
12 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Instrumentation for Astronomy VII

The Maunakea Spectroscopic Explorer (MSE) is replacement of the existing 3.6-m Canada France Hawaii Telescope into a dedicated wide field highly multiplexed fiber fed spectroscopic facility. MSE is capable of observing over four thousand science targets simultaneously in two resolution modes. The paper describes the unique instrument system capabilities and its components starting from the telescope prime focus and ending at the spectrograph suite. The instrument system components have completed their conceptual designs and they include a Sphinx positioner system, fiber transmission system, low/moderate resolution and high resolution spectrographs and a calibration system. These components will be procured separately and the Project is responsible for their integration and the overall system performance afterward. The paper describes from a system perspective the specific design and interface constraints imposed on the components given the extra interface and integration considerations.

[192] arXiv:1807.08014v1 [pdf, vox]

Maunakea Spectroscopic Explorer Advancing from Conceptual Design

Kei Szeto, Doug Simons, Steven Bauman, Alexis Hill, Nicolas Flagey, Alan McConnachie, Shan Mignot, Richard Murowinski
Submitted Friday 20 July 2018 @ 20:11:35 GMT
15 pages; Proceedings of SPIE Astronomical Telescopes + Instrumentation 2018; Ground-based and Airborne Telescopes VII

The Maunakea Spectroscopic Explorer (MSE) project has completed its Conceptual Design Phase. This paper is a status report of the MSE project regarding its technical and programmatic progress. The technical status includes its conceptual design and system performance, and highlights findings and recommendations from the System and various subsystems design reviews. The programmatic status includes the project organization and management plan for the Preliminary Design Phase. In addition, this paper provides the latest information related to the permitting process for Maunakea construction.

[193] arXiv:1807.08010v1 [pdf, vox]

Measurement of the Iron Spectrum in Cosmic Rays by VERITAS

The VERITAS collaboration, A. Archer, W. Benbow, R. Bird, R. Brose, M. Buchovecky, V. Bugaev, M. P. Connolly, W. Cui, M. K. Daniel, A. Falcone, Q. Feng, J. P. Finley, H. Fleischhack, L. Fortson, A. Furniss, D. Hanna, O. Hervet, J. Holder, G. Hughes, T. B. Humensky, M. Hütten, C. A. Johnson, P. Kaaret, N. Kelley-Hoskins, D. Kieda, M. Krause, F. Krennrich, S. Kumar, M. J. Lang, G. Maier, S. McArthur, P. Moriarty, R. Mukherjee, D. Nieto, S. O'Brien, R. A. Ong, A. N. Otte, N. Park, A. Petrashyk, M. Pohl, A. Popkow, E. Pueschel, J. Quinn, K. Ragan, P. T. Reynolds, G. T. Richards, E. Roache, C. Rulten, I. Sadeh, J. Tyler, S. P. Wakely, O. M. Weiner, P. Wilcox, A. Wilhelm, D. A. Williams, S. A. Wissel, B. Zitzer
Submitted Friday 20 July 2018 @ 19:55:40 GMT
16 pages, 5 figures, submitted to Phys. Rev. D

We present a new measurement of the energy spectrum of iron nuclei in cosmic rays from 20 to 500 TeV. The measurement makes use of a template-based analysis method, which, for the first time, is applied to the energy reconstruction of iron-induced air showers recorded by the VERITAS array of imaging atmospheric Cherenkov telescopes. The event selection makes use of the direct Cherenkov light which is emitted by charged particles before the first interaction, as well as other parameters related to the shape of the recorded air shower images. The measured spectrum is well described by a power law $\frac{\mathrm{d} F}{\mathrm{d} E}=f_0\cdot \left(\frac{E}{E_0}\​right)^{-\gamma}$ over the full energy range, with $\gamma = 2.82 \pm 0.30 \mathrm{(stat.)} ^{+0.24}_{-0.27} \mathrm{(syst.)}$ and $f_0 = \left( 4.82 \pm 0.98 \mathrm{(stat.)}^{+2​.12}_{-2.70} \mathrm{(syst.)} \right)\cdot 10^{-7}$m$^{-2}$s$^{​-1}$sr$^{-1}$TeV$^{-​1}$ at $E_0=50$TeV, with no indication of a cutoff or spectral break. The measured differential flux is compatible with previous results, with improved statistical uncertainty at the highest energies.

[194] arXiv:1807.07993v1 [pdf, vox]

Is the Cometary Nucleus Extraction Technique Reliable?

Man-To Hui, Jian-Yang Li
Submitted Friday 20 July 2018 @ 18:29:43 GMT
Accepted by PASP. The last figure in this arXiv version contains two mysterious horizontal and vertical streaks, possibly due to compiling issues

It depends. Our experiment reveals that, given an optically thin coma, generally, the smaller the signal ratio of nucleus to coma, the less reliable is the cometary nucleus-extraction technique. We strongly suggest the technique only be applied to cases where the nucleus signal occupies $\gtrsim$10% of the total signal wherein the bias is no more than a few percent. Otherwise there is probably no way to debias results from this technique in reality, since its reliability is highly sensitive to entangling complications, including the coma profile, and the point-spread function (PSF).

[195] arXiv:1807.07985v1 [pdf, vox]

Mid-IR Variability of Quasars and A Luminous Transient Event in A WISE-Selected AGN

R. J. Assef, J. L. Prieto, D. Stern, R. M. Cutri, P. R. M. Eisenhardt, M. J. Graham, H. D. Jun, A. Rest, H. A. Flewelling, N. Kaiser, R. -P. Kudritzki, C. Waters
Submitted Friday 20 July 2018 @ 18:11:42 GMT
Submitted to The Astrophysical Journal. A version with all Figures from the last appendix can be found at http://www.astro.udp​.cl/~rjassef/Assef_e​t_al_2018_All_Figure​s.pdf

Recently Assef et al.(2018) presented two catalogs of AGN candidates over 30,093 deg^2 selected from the Wide-field Infrared Survey Explorer (WISE) observations. From their most reliable sample, Assef et al. (2018) identified 45 AGN candidates with the highest variability levels in the AllWISE catalog, but that are not blazars. Here we present new spectroscopic observations of some of these targets to further constrain their nature. We also study their optical lightcurves using observations from CRTS, and find that only seven show significant optical variability, and that five of those seven are spectroscopically classified as AGN. In one of them, WISEA J094806.56+031801.7 (W0948+0318), we identify a transient event in the CRTS lightcurve. We present a detailed analysis of this transient, and characterize it through its CRTS lightcurve and its multi-wavelength spectral energy distribution obtained from GALEX, Pan-STARRS and WISE observations. We find that the most likely source of the transient is a super-luminous supernova (SLSN) in W0948+0318. We estimate the total radiated energy to be E=1.6\pm 0.3 x 10^52 erg, making it one of the most energetic SLSN observed. Based on the lack of change in mid-IR color throughout and after the transient event, we speculate that the location of the SLSN is within the torus of the AGN. We identify 9 possible analogs to W0948+0318 based on their WISE lightcurves. None show optically detected transients and hence suggest significant dust obscuration. Finally, we estimate a rate of >2x10^-7 yr^-1 per AGN for these transients under the conservative assumption that none of the identified analogs have a common origin with the transient in W0948+0318.

[196] arXiv:1807.07977v1 [pdf, vox]

The GALAH survey: a catalog of carbon enhanced stars and CEMP candidates

Klemen Čotar, Tomaž Zwitter, Janez Kos, Ulisse Munari, Sarah L. Martell, Martin Asplund, Joss Bland-Hawthorn, Gayandhi M. De Silva, Kenneth C. Freeman, Borja Anguiano, Daniela Carollo, Jonathan Horner, Geraint F. Lewis, David M. Nataf, Thomas Nordlander, Denis Stello, Yuan-Sen Ting, Chris Tinney, Gregor Traven
Submitted Friday 20 July 2018 @ 18:00:21 GMT
12+4 pages, 12 figures, 1 catalog, submitted to MNRAS

Swan bands - characteristic molecular absorption features of the C$_2$ molecule - are a spectroscopic signature of carbon enhanced stars. They can also be used to identify notorious carbon enhanced metal-poor (CEMP) stars. GALAH (GALactic Archaeology with Hermes) is a magnitude limited survey of stars producing high resolution, high signal-to-noise spectra. We use 627.708 GALAH spectra to search for carbon enhanced stars with a supervised and unsupervised classification algorithm, relying on the imprint of the Swan bands. We identified 918 carbon enhanced stars, including 12 already described in the literature. An unbiased selection function of the GALAH survey allows us to perform a population study of carbon enhanced stars. Most of them are giants, out of which we find 28 CEMP candidates. Large fraction of stars with repeated observations show variation in radial velocity, hinting that there is a large fraction of variables among carbon enhanced stars. 32 of detected stars also show strong Lithium enhancement in their spectra.

[197] arXiv:1807.07973v1 [pdf, vox]

Chromatic transit light curves of disintegrating rocky planets

A. R. Ridden-Harper, C. U. Keller, M. Min, R. van Lieshout, I. A. G. Snellen
Submitted Friday 20 July 2018 @ 18:00:03 GMT
22 pages, 22 figures, accepted for publication in A&A

Context. Kepler observations have revealed a class of short period exoplanets, of which Kepler-1520 b is the prototype, which have comet-like dust tails thought to be the result of small, rocky planets losing mass. The shape and chromaticity of the transits constrain the properties of the dust particles originating from the planet's surface, offering a unique opportunity to probe the composition and geophysics of rocky exoplanets. Aims. We aim to approximate the average Kepler long-cadence light curve of Kepler-1520 b and investigate how the optical thickness and transit cross-section of a general dust tail can affect the observed wavelength dependence and depth of transit light curves. Methods. We developed a new 3D model that ejects sublimating particles from the planet surface to build up a dust tail, assuming it to be optically thin, and used 3D radiative transfer computations that fully treat scattering using the distribution of hollow spheres (DHS) method, to generate transit light curves between 0.45 and 2.5 $\mu$m. Results. We show that the transit depth is wavelength independent for optically thick tails, potentially explaining why only some observations indicate a wavelength dependence. From the 3D nature of our simulated tails, we show that their transit cross-sections are related to the component of particle ejection velocity perpendicular to the planet's orbital plane and use this to derive a minimum ejection velocity of 1.2 kms$^{-1}$. To fit the average transit depth of Kepler-1520 b of 0.87%, we require a high dust mas-loss rate of 7 $-$ 80 M$_\oplus$ Gyr$^{-1}$ which implies planet lifetimes that may be inconsistent with the observed sample. Therefore, these mass-loss rates should be considered to be upper limits.

[198] arXiv:1807.07971v1 [pdf, vox]

The physics of multiphase gas flows: fragmentation of a radiatively cooling gas cloud in a hot wind

Martin Sparre, Christoph Pfrommer, Mark Vogelsberger
Submitted Friday 20 July 2018 @ 18:00:01 GMT
Submitted to MNRAS

Galactic winds exhibit a multiphase structure that consists of hot-diffuse and cold-dense phases. Here we present high-resolution idealised simulations of the interaction of a hot supersonic wind with a cold cloud with the moving-mesh code AREPO in setups with and without radiative cooling. We demonstrate that cooling causes clouds with sizes larger than the cooling length to fragment in two- and three-dimensional simulations (2D and 3D). We confirm earlier 2D simulations by McCourt et al. 2018 and highlight differences of the shattering processes of 3D clouds that are exposed to a hot wind. The fragmentation process is quantified with a friends-of-friends analysis of shattered cloudlets and density power spectra. Those show that radiative cooling causes the power spectral index to gradually increase when the initial cloud radius is larger than the cooling length and with increasing time until the cloud is fully dissolved in the hot wind. A resolution of around 1 pc is required to reveal the effect of cooling-induced fragmentation of a 100 pc outflowing cloud. Thus, state-of-the-art cosmological zoom simulations of the circumgalactic medium (CGM) fall short by orders of magnitudes from resolving this fragmentation process. This physics is, however, necessary to reliably model observed column densities and covering fractions of Lyman-alpha haloes, high-velocity clouds, and broad-line regions of active galactic nuclei.

[199] arXiv:1807.07970v1 [pdf, vox]

Simulating the Magnetorotational Collapse of Supermassive Stars: Incorporating Gas Pressure Perturbations and Different Rotation Profiles

Lunan Sun, Milton Ruiz, Stuart L. Shapiro
Submitted Friday 20 July 2018 @ 18:00:00 GMT
16 pages, 7 figures

Collapsing supermassive stars (SMSs) with masses $M \gtrsim 10^{4-6}M_\odot$ have long been speculated to be the seeds that can grow and become supermassive black holes (SMBHs). We previously performed GRMHD simulations of marginally stable magnetized $\Gamma = 4/3$ polytropes uniformly rotating at the mass-shedding limit to model the direct collapse of SMSs. These configurations are supported entirely by thermal radiation pressure and model SMSs with $M \gtrsim 10^{6}M_\odot$. We found that around $90\%$ of the initial stellar mass forms a spinning black hole (BH) surrounded by a massive, hot, magnetized torus, which eventually launches an incipient jet. Here we perform GRMHD simulations of $\Gamma \gtrsim 4/3$, polytropes to account for the perturbative role of gas pressure in SMSs with $M \lesssim 10^{6}M_\odot$. We also consider different initial stellar rotation profiles. The stars are initially seeded with a dynamically weak dipole magnetic field that is either confined to the stellar interior or extended from its interior into the stellar exterior. We find that the mass of the BH remnant is $90\%-99\%$ of the initial stellar mass, depending sharply on $\Gamma -4/3$ as well as on the initial stellar rotation profile. After $t\sim 250-550M\approx 1-2\times 10^3(M/10^6M_\odot)$​s following the BH formation, a jet is launched and it lasts for $\sim 10^4-10^5(M/10^6M_\o​dot)$s, consistent with the duration of long gamma-ray bursts. Our results suggest that the Blandford-Znajek mechanism powers the jet. They are also in agreement with our proposed universal model that estimates accretion rates and luminosities that characterize magnetized BH-disk remnant systems that launch a jet. This model helps explain why the outgoing luminosities for vastly different BH-disk formation scenarios all reside within a narrow range ($\sim 10^{52 \pm 1} \rm erg/s$), roughly independent of $M$.

[200] arXiv:1807.07956v1 [pdf, vox]

Strength, stability and three dimensional structure of mean motion resonances in the Solar System

Tabare Gallardo
Submitted Friday 20 July 2018 @ 17:58:11 GMT

In the framework of the circular restricted three body problem we show that the numerically computed strength SR(e,i,w) is a good indicator of the strength and width of the mean-motion resonances in the full space (e,i,w). We present a survey of strengths in the space (e,i) for typical interior and exterior resonances. The resonance strength is highly dependent on (e,i,w) except for exterior resonances of the type 1:k for which the dependence with (i,w) is softer. Such resonances are thus strong even for retrograde orbits. All other resonances are weaker at very-high eccentricities for w ~ 90 or 270 and 60 < i < 120. We explore the resonance structure in the space (a,i) by means of dynamical maps and we find structures similar to those of space (a,e).

[201] arXiv:1807.07955v1 [pdf, vox]

New Young Stars and Brown Dwarfs in the Upper Scorpius Association

K. L. Luhman, K. A. Herrmann, E. E. Mamajek, T. L. Esplin, M. J. Pecaut
Submitted Friday 20 July 2018 @ 17:56:45 GMT
Astronomical Journal, in press; machine readable tables and fits spectra available at http://personal.psu.​edu/kll207/usco.tar

To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.

[202] arXiv:1807.07947v1 [pdf, vox]

Pre-maximum and maximum of Novae: The spectroscopic observations of Nova ASASSN-17hx

Rosa Poggiani
Submitted Friday 20 July 2018 @ 17:34:14 GMT
Proceedings of a talk given at the conference "The Golden Age of Cataclysmic Variables and Related Objects IV (GOLDEN 2017)", 11-16 September, 2017, Palermo, Italy; 9 pages, 8 figures

The coverage of the pre-maximum stage of novae is sparse, with the exception of a few slow novae where the pre-maximum duration is of the order of some weeks. This paper discusses the main features of novae during the pre-maximum and the maximum stages and reports the preliminary results of an investigation of ASASSN-17hx, a peculiar nova that showed a long pre-maximum and secondary brightenings.

[203] arXiv:1807.07944v1 [pdf, vox]

The Maxwell's demon of star clusters

Michela Mapelli
Submitted Friday 20 July 2018 @ 17:26:07 GMT
17 pages, 8 figures, Submitted Manuscript Under Review: To appear in The Impact of Binaries on Stellar Evolution, Beccari G. & Boffin H.M.J. (Eds.).\copyright\ 2018 Cambridge University Press

Stellar binaries are the most important energy reservoir of star clusters. Via three-body encounters, binaries can reverse the core collapse and prevent a star cluster from reaching equipartition. Moreover, binaries are essential for the formation of stellar exotica, such as blue straggler stars, intermediate-mass black holes and massive ($\gtrsim{}30$ M$_\odot$) black hole binaries.

[204] arXiv:1807.07942v1 [pdf, vox]

VLBI radio structure and core-brightening of the high-energy neutrino emitter TXS 0506+056

E. Kun, P. L. Biermann, L. Á. Gergely
Submitted Friday 20 July 2018 @ 17:13:46 GMT
5 pages, 4 figures

We report on the radio-brightening of the blazar TXS 0506+056 in temporal coincidence with the IC-170922A high-energy neutrino detection by the IceCube Neutrino Observatory. Very long baseline interferometry (VLBI) data at 15 GHz spanning 16 epochs between January 2009 and May 2018 were analysed in order to reveal the radio structure of the blazar TXS 0506+056 (z=0.3365). This flaring $\gamma$-ray blazar has been recently identified as the source of the high-energy neutrino event IC-170922A, also supported by the excess of cosmic neutrinos between September 2014 and March 2015 reported by the IceCube Collaboration. Our investigations indicate that the radio flux density of the TXS 0506+056 VLBI core has been abruptly brightening since January 2016, producing an accumulated fourfold increase until the most recent observation. Further, the radio jet-components maintain peculiar quasi-stationary core separations and the structure of the jet ridge line, as well as the flux density variation along it is indicative of a jet curve at the region $0.5-2$ mas from the VLBI core. These features support a helical jet structure and a small inclination angle, which is less than $7^\circ$ based on the average brightness temperature of the core. The radio jet pointing towards the Earth is the key property of the blazar TXS 0506+056 enabling multimessenger observations. The radio-brightening coincident with the high-energy neutrino detection is similar to the one reported for the blazar PKS 0723-008 and IceCube event ID5.

[205] arXiv:1807.07938v1 [pdf, vox]

Sterile Neutrino Dark Matter

A. Boyarsky, M. Drewes, T. Lasserre, S. Mertens, O. Ruchayskiy
Submitted Friday 20 July 2018 @ 16:54:19 GMT
Invited review to appear in Progress in Particle and Nuclear Physics. 59 pages, 14 figures

We review sterile neutrinos as possible Dark Matter candidates. After a short summary on the role of neutrinos in cosmology and particle physics, we give a comprehensive overview of the current status of the research on sterile neutrino Dark Matter. First we discuss the motivation and limits obtained through astrophysical observations. Second, we review different mechanisms of how sterile neutrino Dark Matter could have been produced in the early universe. Finally, we outline a selection of future laboratory searches for keV-scale sterile neutrinos, highlighting their experimental challenges and discovery potential.

[206] arXiv:1807.07913v1 [pdf, vox]

Tilt of sunspot bipoles in Solar Cycles 15 to 24

Ksenia Tlatova, Andrey Tlatov, Alexei Pevtsov, Kalevi Mursula, Valeria Vasil'eva, Elina Heikkinen, Luca Bertello, Alexander Pevtsov, Ilpo Virtanen, Nina Karachik
Submitted Friday 20 July 2018 @ 16:04:59 GMT
14 pages, 5 figures, accepted for publication in Solar Physics

We use recently digitized sunspot drawings from Mount Wilson Observatory to investigate the latitudinal dependence of tilt angles of active regions and its change with solar cycle. The drawings cover the period from 1917 to present and contain information about polarity and strength of magnetic field in sunspots. We identify clusters of sunspots of same polarity, and used these clusters to form ``bipole pairs''. The orientation of these bipole pairs was used to measure their tilts. We find that the latitudinal profile of tilts does not monotonically increase with latitude as most previous studies assumed, but instead, it shows a clear maximum at about 25--30 degree latitudes. Functional dependence of tilt ($\gamma$) on latitude ($\varphi$) was found to be $\gamma = (0.20\pm 0.08) \sin (2.80 \varphi) + (-0.00\pm 0.06)$. We also find that latitudinal dependence of tilts varies from one solar cycle to another, but larger tilts do not seem to result in stronger solar cycles. Finally, we find the presence of a systematic offset in tilt of active regions (non-zero tilts at the equator), with odd cycles exhibiting negative offset and even cycles showing the positive offset.

[207] arXiv:1807.07912v1 [pdf, vox]

Fabrication of low-cost, large-area prototype Si(Li) detectors for the GAPS experiment

Kerstin Perez, Tsuguo Aramaki, Charles J. Hailey, Rachel Carr, Tyler Erjavec, Hideyuki Fuke, Amani Garvin, Cassia Harper, Glenn Kewley, Norman Madden, Sarah Mechbal, Field Rogers, Nathan Saffold, Gordon Tajiri, Katsuhiko Tokuda, Jason Williams, Minoru Yamada
Submitted Friday 20 July 2018 @ 16:02:22 GMT
Accepted for publication at Nuclear Instrumentation and Methods A, 12 pages, 11 figures

A Si(Li) detector fabrication procedure has been developed with the aim of satisfying the unique requirements of the GAPS (General Antiparticle Spectrometer) experiment. Si(Li) detectors are particularly well-suited to the GAPS detection scheme, in which several planes of detectors act as the target to slow and capture an incoming antiparticle into an exotic atom, as well as the spectrometer and tracker to measure the resulting decay X-rays and annihilation products. These detectors must provide the absorption depth, energy resolution, tracking efficiency, and active area necessary for this technique, all within the significant temperature, power, and cost constraints of an Antarctic long-duration balloon flight. We report here on the fabrication and performance of prototype 2"-diameter, 1-1.25 mm-thick, single-strip Si(Li) detectors that provide the necessary X-ray energy resolution of $\sim$4 keV for a cost per unit area that is far below that of previously-acquired commercial detectors. This fabrication procedure is currently being optimized for the 4"-diameter, 2.5 mm-thick, multi-strip geometry that will be used for the GAPS flight detectors.

[208] arXiv:1807.07905v1 [pdf, vox]

Electromagnetic emission of WD-WD mergers

J. A. Rueda, R. Ruffini, Y. Wang, C. L. Bianco, J. M. Blanco-Iglesias, M. Karlica, P. Loren-Aguilar, R. Moradi, N. Sahakyan
Submitted Friday 20 July 2018 @ 15:47:04 GMT
8 pages, submitted to A&A

CONTEXT: It has been recently advanced the proposal that the ejected matter from white dwarf (WD) binary mergers might produce transient optical and infrared emission similar to the "kilonovae" of neutron star (NS) binary mergers. AIMS: To calculate the electromagnetic emission from the WD-WD mergers and compare with kilonova observations. METHODS: We simulate WD-WD mergers leading to a massive, fast rotating, highly magnetized WD with an adapted version of the smoothed-particle-hy​drodynamics (SPH) code Phantom. We thus obtain initial conditions for the ejecta such as escape velocity, mass and initial position and distribution. The subsequent thermal and dynamical evolution of the ejecta is obtained by integrating the energy-conservation equation accounting for expansion cooling and a heating source given by the fallback accretion onto the newly-formed WD and its magneto-dipole radiation. RESULTS: We apply our model to the most detailed observed kilonova, AT 2017gfo, and its associated gamma-ray burst (GRB) 170817A. We show that magnetospheric processes in the merger can lead to a prompt, short gamma-ray emission of up to 10^{46}erg in a timescale of 0.1-1s. The ejecta bulk starts the expansion with a non-relativistic velocity 0.01c and then accelerates to 0.1c owing to the fallback accretion energy injection which dominates over the spindown energy. The ejecta expands to become transparent in the optical wavelengths at ~7 days post-merger with a luminosity 10^{41}-10^{42}erg/s​. The transparency to the X-rays from the ongoing fallback accretion occurs at ~150-200 day post-merger with a luminosity of 10^{39}erg/s. CONCLUSIONS: We show that WD-WD mergers can lead to electromagnetic emission as the one observed in GRB 170817A-AT 2017gfo. We also predict the post-merger time at which the central WD should appear as a pulsar depending on the value of the magnetic field and rotation period.

[209] arXiv:1807.07904v1 [pdf, vox]

Observational signatures of dark energy produced in an ancestor vacuum: Forecast for galaxy surveys

Daisuke Yamauchi, Hajime Aoki, Satoshi Iso, Da-Shin Lee, Yasuhiro Sekino, Chen-Pin Yeh
Submitted Friday 20 July 2018 @ 15:40:51 GMT
5 pages, 2 figures

We study observational consequences of the model for dark energy proposed in [1] (Aoki et al., Phys.Rev. D97 (2018) no.4, 043517). We assume our universe has been created by bubble nucleation, and consider quantum fluctuations of an ultralight scalar field. Residual effects of fluctuations generated in an ancestor vacuum (de Sitter space in which the bubble was formed) is interpreted as dark energy. Its equation of state parameter w(z) has a characteristic form, approaching -1 in the future, but -1/3 in the past. A novel feature of our model is that dark energy effectively increases the magnitude of the negative spatial curvature in the evolution of the Hubble parameter, though it does not alter the definition of the angular diameter distance. We perform Fisher analysis and forecast the constraints for our model from future galaxy surveys by Square Kilometre Array and Euclid. Due to degeneracy between dark energy and the spatial curvature, galaxy surveys alone can determine these parameters only for optimistic choices of their values, but combination with other independent observations, such as CMB, will greatly improve the chance of determining them.

[210] arXiv:1807.07899v1 [pdf, vox]

The role of galaxies and AGN in reionizing the IGM - II: metal-tracing the faint sources of reionization at $5\lesssim z\lesssim6$

Romain A. Meyer, Sarah E. I. Bosman, Koki Kakiichi, Richard S. Ellis
Submitted Friday 20 July 2018 @ 15:36:45 GMT
19 pages, 11 figures, submitted to MNRAS

We present a new method to study the contribution of faint sources to the UV background using the cross-correlation of metal absorbers with the intergalactic medium (IGM) transmission in a proximate Quasi Stellar Object (QSO) sightline. We take advantage of a sample of $25$ high signal-to-noise ratio QSO spectra to retrieve $146$ triply-ionised carbon (\cfour) absorbers at $4.5\lesssim z\lesssim 6.2$, of which $37$ systems whose expected H{~\small I} absorption lie in the Lyman-$\alpha$ forest. We derive improved constraints on the cosmic density of \cfour \,at $4.3< z < 6.2$ and infer from abundance-matching that \cfour \,absorbers trace $M_{\text{UV}}\lesss​im -16$ galaxies. Cross-correlation with the Lyman-$\alpha$ forest of the QSOs indicates that these objects are surrounded by a highly opaque region of neutral hydrogen to $r\lesssim 5 $ cMpc/h followed by an excess of transmission at $r\gtrsim 10$ cMpc/h detected at $2.7\sigma$. This is in contrast to equivalent measurements at lower redshifts where only the opaque trough is detected. We interpret this excess as a statistical enhancement of the local photoionisation rate due to clustered faint galaxies around the \cfour \,absorbers. Using the analytical framework described in Paper I of this series, we derive a constraint on the average product of the escape fraction and the Lyman continuum photon production efficiency of the galaxy population clustered around the \cfour \,absorbers, $\log \langle f_{\text{esc}}\xi_{\​text{ion}}\rangle /[{\rm erg^{-1}~Hz}] = 25.01^{+0.30}_{-0.19​}$. This implies that faint galaxies beyond the reach of current facilities may have harder radiation fields and/or larger escape fractions than currently detected objects at the end of the reionisation epoch.

[211] arXiv:1807.07895v1 [pdf, vox]

A WISE Survey of Circumstellar disks in the Upper Scorpius Association

T. L. Esplin, K. L. Luhman, E. B. Miller, E. E. Mamajek
Submitted Friday 20 July 2018 @ 15:34:58 GMT
Accepted for publication in AJ. Associated tables and spectra can be found at https://www.dropbox.​com/sh/52ygee5v3x6te​9a/AABZm55PAI44EMQKv​OjsDRxAa?dl=0

We have performed a survey for new members of the Upper Sco association that have circumstellar disks using mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE). Through optical and near-infrared spectroscopy, we have confirmed 185 candidates as likely members of Upper Sco with spectral types ranging from mid-K to M9. They comprise ~36% of the known disk-bearing members of the association. We also have compiled all available mid-infrared photometry from WISE and the Spitzer Space Telescope for the known members of Upper Sco, resulting in a catalog of data for 1608 objects. We have used these data to identify the members that exhibit excess emission from disks and we have classified the evolutionary stages of those disks with criteria similar to those applied in our previous studies of Taurus and Upper Sco. Among 484 members with excesses in at least one band (excluding five Be stars), we classify 296 disks as full, 66 as evolved, 19 as transitional, 22 as evolved or transitional, and 81 as evolved transitional or debris. Many of these disks have not been previously reported, including 129 full disks and 50 disks that are at more advanced evolutionary stages.

[212] arXiv:1807.07894v1 [pdf, vox]

The edge of space: Revisiting the Karman Line

Jonathan C. McDowell
Submitted Friday 20 July 2018 @ 15:33:07 GMT
17 pages, 4 figures

In this paper I revisit proposed definitions of the boundary between the Earth's atmosphere and outer space, considering orbital and suborbital trajectories used by space vehicles. In particular, I investigate the inner edge of outer space from historical, physical and technological viewpoints and propose 80 kilometers as a more appropriate boundary than the currently popular 100 km Von K\'{a}rm\'{a}n line.

[213] arXiv:1807.07859v1 [pdf, vox]

The Type II Superluminous SN 2008es at Late Times: Near-Infrared Excess and Circumstellar Interaction

Kornpob Bhirombhakdi, Ryan Chornock, Adam A. Miller, Alexei V. Filippenko, S. Bradley Cenko, Nathan Smith
Submitted Friday 20 July 2018 @ 14:23:40 GMT

SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN) showing no relatively narrow features in its early-time spectra, and therefore its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 days after explosion. Only broad H$\alpha$ emission is detected in a Gemini spectrum at 288 days. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, a NIR excess with blackbody temperature $\sim1500$ K and radius $\sim10^{16}$ cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with $\sim2$--3 $\textrm{M}_\odot$ of circumstellar material (CSM) and $\sim$10--20 $\textrm{M}_\odot$ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius $\sim 10^{15}$ cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount ($\lesssim 0.4$ $\textrm{M}_\odot$) of $^{56}$Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust.

[214] arXiv:1807.07852v1 [pdf, vox]

Schwarzschild dynamical model of the Fornax dwarf spheroidal galaxy

Klaudia Kowalczyk, Andrés del Pino, Ewa L. Lokas, Monica Valluri
Submitted Friday 20 July 2018 @ 14:10:19 GMT
10 pages, 8 figures, 3 tables, submitted to MNRAS

We present a full dynamical model of the Fornax dwarf spheroidal galaxy obtained with the spherically symmetric Schwarzschild orbit superposition method applied to the largest kinematic data set presently available. We modelled the total mass content of the dwarf with the mass-to-light ratio $\Upsilon$ varying with radius and found that Fornax is with high probability embedded in a massive and extended dark matter halo. We estimated the total mass contained within 1$\,$kpc to be $M(<1\,$kpc$)=1.25^{​+0.06}_{-0.13} \times 10^8\,$M$_{\odot}$. The data are consistent with the constant mass-to-light ratio, i.e. the mass-follows-light model, only at 3$\sigma$ level, but still require a high value of $\Upsilon \approx 11.2\,$M$_{\odot}/$L​$_{\odot}$. Our results are in general agreement with previous estimates of the dynamical mass profile of Fornax. As the Schwarzschild method does not require any assumptions on the orbital anisotropy of the stars, we obtained a profile of the anisotropy parameter $\beta$ as an output of our modelling. The derived anisotropy is close to zero in the centre of the galaxy and decreases with radius, but remains consistent with isotropic orbits at all radii at 1$\sigma$ confidence level.

[215] arXiv:1807.07834v1 [pdf, vox]

CUTE Data Simulator and Reduction Pipeline

A. G. Sreejith, Luca Fossati, Manfred Steller, Brian T. Fleming, Kevin France
Submitted Friday 20 July 2018 @ 13:34:14 GMT
Proceedings Volume 10699, Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray; 1069932 (2018)

The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U NASA CubeSat carrying a low-resolution (R ~3000), near-ultraviolet (255 - 330nm) spectrograph fed by a rectangular primary Cassegrain. CUTE, is planned for launch in spring 2020 and it will monitor transiting extra-solar planets to study atmospheric escape. We present here the CUTE data simulator, which is a versatile tool easily adaptable to any other mission performing single-slit spectroscopy and carrying on-board a CCD detector. We complemented the data simulator with a data reduction pipeline capable of performing a rough reduction of the simulated data. This pipeline will then be updated once the final CUTE data reduction pipeline will be fully developed. We further briefly discuss our plans for the development of a CUTE data reduction pipeline. The data simulator will be used to inform the target selection, improve the preliminary signal-to-noise calculator, test the impact on the data of deviations from the nominal instrument characteristics, identify the best spacecraft orientation for the observation of each target and construct synthetic data to train the science team in the data analysis prior to launch.

[216] arXiv:1807.08631v1 [pdf, vox]

Classical and relativistic laws of motion for spherical supernovas

Lorenzo Zaninetti
Submitted Friday 20 July 2018 @ 12:29:32 GMT
35 Pages and 17 low quality figures. arXiv admin note: substantial text overlap with arXiv:1410.5193

We derive some first order differential equations which model the classical and the relativistic thin layer approximations. The circumstellar medium is assumed to follow a density profile which can be exponential, Gaussian, Plummer-like, self-gravitating of Lane--Emden ($n=5$) type, or power law. The first order differential equations are solved analytically, or numerically, or by a series expansion, or by recursion, or by Pad\'e approximation. The initial conditions are chosen in order to model the temporal evolution of SN 1993J over ten years. The Pad\'e approximated equations of motion are applied to four SNRs: Tycho, Cas A, Cygnus loop, and SN~1006.

[217] arXiv:1807.07733v1 [pdf, vox]

Zoomable telescope by rotation of toroidal lenses

Stefan Bernet
Submitted Friday 20 July 2018 @ 08:10:24 GMT

A novel type of a continuously zoomable telescope is based on two pairs of adjacent toroidal lenses ("saddle lenses") in combination with standard optical components. Its variable magnification is adjusted by a mere rotation of the four saddle lenses around the optical axis. This avoids the necessity of classical zoom systems to shift multiple lenses along the longitudinal axis of the setup. A rotationally tunable pair of saddle lens consists of two individual saddle lenses (also known as quadrupole lenses, or biconic lenses), which are arranged directly behind each other, acting as a "combi-saddle lens". The transmission function of such a combi-saddle lens corresponds to that of a single saddle lens, but with an adjustable optical power which depends on the mutual rotation angle between its two components. The optical system contains two of these combi-saddle lenses, and acts as a cylindrical Kepler telescope in one plane, and as a cylindrical Galilei telescope in the orthogonal plane. The two orthogonal Kepler/Galilei telescopes stay aligned and change their magnification factors in the same way when the telescope is zoomed by adjusting the optical powers of the two combi-saddle lenses. Altogether this produces a sharp image which is mirrored with respect to the axis of the Kepler telescope. Thus, in addition to the zooming capabilities of the telescope, it is also possible to rotate the resulting image by a rotation of the whole telescope, or of all included saddle lenses. We theoretically explain the operation principle of the telescope in both, a ray-optical and a wave-optical description.

[218] arXiv:1807.07723v1 [pdf, vox]

Vialactea Visual Analytics tool for Star Formation studies of the Galactic Plane

F. Vitello, E. Sciacca, U. Becciani, A. Costa, M. Bandieramonte, M. Benedettini, M. Brescia, R. Butora, S. Cavuoti, A. M. Di Giorgio, D. Elia, S. J. Liu, S. Molinari, M. Molinaro, G. Riccio, E. Schisano, R. Smareglia
Submitted Friday 20 July 2018 @ 07:36:03 GMT

We present a visual analytics tool, based on the VisIVO suite, to exploit a combination of all new-generation surveys of the Galactic Plane to study the star formation process of the Milky Way. The tool has been developed within the VIALACTEA project, founded by the 7th Framework Programme of the European Union, that creates a common forum for the major new-generation surveys of the Milky Way Galactic Plane from the near infrared to the radio, both in thermal continuum and molecular lines. Massive volumes of data are produced by space missions and ground-based facilities and the ability to collect and store them is increasing at a higher pace than the ability to analyze them. This gap leads to new challenges in the analysis pipeline to discover information contained in the data. Visual analytics focuses on handling these massive, heterogeneous, and dynamic volumes of information accessing the data previously processed by data mining algorithms and advanced analysis techniques with highly interactive visual interfaces offering scientists the opportunity for in-depth understanding of massive, noisy, and high-dimensional data.

[219] arXiv:1807.07714v1 [pdf, vox]

Photospheric Shear Flows in Solar Active Regions and Their Relation to Flare Occurrence

Sung-Hong Park, Jordan A. Guerra, Peter T. Gallagher, Manolis K. Georgoulis, D. Shaun Bloomfield
Submitted Friday 20 July 2018 @ 06:56:20 GMT
19 pages, 8 figures, accepted for publication in Solar Physics

Solar active regions (ARs) that produce major flares typically exhibit strong plasma shear flows around photospheric magnetic polarity inversion lines (MPILs). It is therefore important to quantitatively measure such photospheric shear flows in ARs for a better understanding of their relation to flare occurrence. Photospheric flow fields were determined by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method to a large data set of 2,548 co-aligned pairs of AR vector magnetograms with 12-min separation over the period 2012-2016. From each AR flow-field map, three shear-flow parameters were derived corresponding to the mean (<S>), maximum (S_max) and integral (S_sum) shear-flow speeds along strong-gradient, strong-field MPIL segments. We calculated flaring rates within 24 hr as a function of each shear-flow parameter, and also investigated the relation between the parameters and the waiting time ({\tau}) until the next major flare (class M1.0 or above) after the parameter observation. In general, it is found that the larger S_sum an AR has, the more likely it is for the AR to produce flares within 24 hr. It is also found that among ARs which produce major flares, if one has a larger value of S_sum then {\tau} generally gets shorter. These results suggest that large ARs with widespread and/or strong shear flows along MPILs tend to not only be more flare productive, but also produce major flares within 24 hr or less.

[220] arXiv:1807.07702v1 [pdf, vox]

Thermal disequilibration of ions and electrons by collisionless plasma turbulence

Yohei Kawazura, Michael Barnes, Alexander A. Schekochihin
Submitted Friday 20 July 2018 @ 03:19:46 GMT

Does overall thermal equilibrium exist between ions and electrons in a weakly collisional, magnetised, turbulent plasma---and, if not, how is thermal energy partitioned between ions and electrons? This is a fundamental question in plasma physics, the answer to which is also crucial for predicting the properties of far-distant astronomical objects such as accretion discs around black holes. In the context of discs, this question was posed nearly two decades ago and has since generated a sizeable literature. Here we provide the answer for the case in which energy is injected into the plasma via Alfv\'enic turbulence: collisionless turbulent heating typically acts to disequilibrate the ion and electron temperatures. Numerical simulations using a hybrid fluid-gyrokinetic model indicate that the ion-electron heating-rate ratio is an increasing function of the thermal-to-magnetic energy ratio, $\beta_\mathrm{i}$: it ranges from $\sim0.05$ at $\beta_\mathrm{i}=0.​1$ to at least $30$ for $\beta_\mathrm{i} \gtrsim 10$. This energy partition is approximately insensitive to the ion-to-electron temperature ratio $T_\mathrm{i}/T_\mat​hrm{e}$. Thus, in the absence of other equilibrating mechanisms, a collisionless plasma system heated via Alfv\'enic turbulence will tend towards a nonequilibrium state in which one of the species is significantly hotter than the other, viz., hotter ions at high $\beta_\mathrm{i}$, hotter electrons at low $\beta_\mathrm{i}$. Spectra of electromagnetic fields and the ion distribution function in 5D phase space exhibit an interesting new magnetically dominated regime at high $\beta_i$ and a tendency for the ion heating to be mediated by nonlinear phase mixing (``entropy cascade'') when $\beta_\mathrm{i}\le​sssim1$ and by linear phase mixing (Landau damping) when $\beta_\mathrm{i}\gg​1$

[221] arXiv:1807.07698v1 [pdf, vox]

Extracting Nuclear Symmetry Energies at High Densities from Observations of Neutron Stars and Gravitational Waves

Nai-Bo Zhang, Bao-An Li
Submitted Friday 20 July 2018 @ 02:40:11 GMT
17 pages prepared for the EPJA Topical Issue: The first Neutron Star Merger Observation - Implications for Nuclear Physics, Eds. David Blaschke, Monica Colpi, Charles Horowitz and David Radice

By numerically inverting the Tolman-Oppenheimer-V​olkov (TOV) equation using an explicitly isospin-dependent parametric Equation of State (EOS) of dense neutron-rich nucleonic matter, a restricted EOS parameter space is established using observational constraints on the radius, maximum mass, tidal polarizability and causality condition of neutron stars (NSs). The constraining band obtained for the pressure as a function of energy (baryon) density is in good agreement with that extracted recently by the LIGO+Virgo Collaborations from their improved analyses of the NS tidal polarizability in GW170817. Rather robust upper and lower boundaries on nuclear symmetry energies are extracted from the observational constraints up to about twice the saturation density $\rho_0$ of nuclear matter. More quantitatively, the symmetry energy at $2\rho_0$ is constrained to $E_{\rm{sym}}(2\rho_​0)=46.9\pm10.1$ MeV excluding many existing theoretical predictions scattered between $E_{\rm{sym}}(2\rho_​0)=15$ and 100 MeV. Moreover, by studying variations of the causality surface where the speed of sound equals that of light at central densities of the most massive neutron stars within the restricted EOS parameter space, the absolutely maximum mass of neutron stars is found to be 2.40 M$_{\odot}$ approximately independent of the EOSs used. This limiting mass is consistent with findings of several recent analyses and numerical general relativity simulations about the maximum mass of the possible super-massive remanent produced in the immediate aftermath of GW170817.

[222] arXiv:1807.07684v1 [pdf, vox]

The Surface Magnetic Activity of the Weak-Line T Tauri Stars TWA 9A and V1095 Sco

B. A. Nicholson, G. A. J. Hussain, J. -F. Donati, C. P. Folsom, M. Mengel, B. D. Carter, D. Wright, the MaTYSSE collaboration
Submitted Friday 20 July 2018 @ 01:26:54 GMT
14 Pages, 17 Figures. Accepted to MNRAS 2018 July 16

We present a detailed analysis of high-resolution spectropolarimetric observations of the weak-line T Tauri stars (wTTSs) TWA 9A and V1095 Sco as part of a wider sur- vey of magnetic properties and activity in weak-line T Tauri stars, called MaTYSSE (Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets). Our targets have similar masses but differing ages which span the stage of radiative core formation in solar-mass stars. We use the intensity line profiles to reconstruct surface brightness maps for both stars. The reconstructed brightness maps for TWA 9A and V1095 Sco were used to model and subtract the activity-induced jitter, reducing the RMS in the radial velocity measurements of TWA 9A by a factor of $\sim$7, and for V1095 Sco by a factor of $\sim$3. We detect significant circular polarisation for both stars, but only acquired a high quality circular polarisation time-series for TWA 9A. Our reconstructed large-scale magnetic field distribution of TWA 9A indicates a strong, non-axisymmetric field. We also analyse the chromospheric activity of both stars by investigating their H$\alpha$ emission, finding excess blue-ward emission for most observations of V1095 Sco, and symmetric, double-peaked emission for TWA 9A, with enhanced emission at one epoch likely indicating a flaring event.

[223] arXiv:1807.07679v1 [pdf, vox]

Blue straggler stars beyond the Milky Way. III. Detection of evolved blue straggler candidates in Large Magellanic Cloud clusters

Chengyuan Li, Licai Deng, Kenji Bekki, Jongsuk Hong, Richard de Grijs, Bi-Qing For
Submitted Friday 20 July 2018 @ 01:03:17 GMT
19 pages, 17 figures, AJ accepted

We analyze {\sl Hubble Space Telescope} observations of nine Large Magellanic Cloud star clusters with ages of 1--2 Gyr to search for evolved counterparts of blue straggler stars. Near the red clump regions in the clusters' color--magnitude diagrams, we find branches of evolved stars that are much brighter than normal evolved stars. We examine the effects of photometric artifacts, differential reddening, and field contamination. We conclude that these bright evolved stars cannot be explained by any of these effects. Our statistical tests show that the contributions of photometric uncertainties and crowding effects, as well as that owing to differential reddening, to these bright evolved stars are insufficient to fully explain the presence of these bright evolved stars. Based on isochrone fitting, we also ruled out the possibility that these bright evolved stars could be reproduced by an internal chemical abundance spread. The spatial distributions of the bright evolved stars exhibit clear concentrations that cannot be explained by homogeneously distributed field stars. This is further confirmed based on Monte Carlo-based tests. By comparing our observations with stellar evolution models, we find that the masses of most of bright evolved stars do not exceed twice the average mass of normal evolved stars. We suggest that these bright evolved stars are, in fact, evolved blue straggler stars.

[224] arXiv:1807.07451v2 [pdf, vox]

$H_0$ tension and the de Sitter Swampland

Eoin Ó Colgáin, Maurice H. P. M. van Putten, Hossein Yavartanoo
Submitted Friday 20 July 2018 @ 00:44:41 GMT
v1 4 pages, comments welcome; v2 replacing mistakenly uploaded unfinished version

Local measurements of the Hubble constant $H_0$ are at odds with $\Lambda$CDM analysis of Planck data and this tension is increasing. This suggests the presence of potentially new physics beyond $\Lambda$CDM. Recently, it has been conjectured that de Sitter vacua inhabit the Swampland of inconsistent low-energy effective theories coupled to gravity. Viewing this proposal through the prism of data, we abandon the notion of stable de Sitter vacua, which allows us to alleviate the $H_0$ tension, but at the cost of violating the Swampland criteria.

Submitted Thu, 19 Jul 2018

[225] arXiv:1807.07668v1 [pdf, vox]

Survival of non-coplanar, closely-packed planetary systems after a close encounter

David R. Rice, Frederic A. Rasio, Jason H. Steffen
Submitted Thursday 19 July 2018 @ 23:59:04 GMT
9 pages, 10 figures, 1 table, Submitted to MNRAS

Planetary systems with more than two bodies will experience orbital crossings at a time related to the initial orbital separations of the planets. After a crossing, the system enters a period of chaotic evolution ending in the reshaping of the system's architecture via planetary collisions or ejections. We carry out N-body integrations on a large number of systems with equally-spaced planets (in units of the Hill radius) to determine the distribution of instability times for a given planet separation. We investigate both the time to the initiation of instability through a close encounter and the time to a planet-planet collision. We find that a significant portion of systems with non-zero mutual inclinations survive after a close encounter and do not promptly experience a planet-planet collision. Systems with significant inclinations can continue to evolve for over 1,000 times longer than the encounter time. The fraction of long lived systems is dependent on the absolute system scale and the initial inclination of the planets. These results have implications to the assumed stability of observed planetary systems.

[226] arXiv:1807.07660v1 [pdf, vox]

An independent search of gravitational waves in the first observation run of advanced LIGO using cross-correlation

Javier M. Antelis, Claudia Moreno
Submitted Thursday 19 July 2018 @ 23:09:10 GMT
12 pages, 6 figures, 1 table

This work describes a template-free method to search gravitational waves (GW) using data from the LIGO observatories simultaneously. The basic idea of this method is that a GW signal is present in a short-duration data segment if the maximum correlation-coeffici​ent between the strain signals is higher than a significant threshold and its time difference is lower than the 10 ms of inter-observatory light propagation time. Hence, this method can be used to carry out blind searches of any types of GW irrespective of the waveform and of the source type and sky location. An independent search of injected and real GW signals from compact binary coalescences (CBC) contained in the first observation run (O1) of advanced LIGO was carried out to asses its performance. On the basis of the results, the proposed method was able to detect GW produced by binary systems without making any assumption about them.

[227] arXiv:1807.07659v1 [pdf, vox]

A consistent estimate for Gravitational Wave and Electromagnetic transient rates

J. J. Eldridge, E. R. Stanway, Petra N. Tang
Submitted Thursday 19 July 2018 @ 22:56:15 GMT
Submitted to MNRAS, 10 pages, 5 figures, 1 table

Gravitational wave transients, resulting from the merger of two stellar remnants, are now detectable. The properties and rates of these directly relates to the stellar population which gave rise to their progenitors, and thus to other, electromagnetic transients which result from stellar death. We aim to estimate simultaneously the event rates and delay time distribution of gravitational wave-driven compact object mergers together with the rates of core collapse and thermonuclear supernovae within a single consistent stellar population synthesis paradigm. We combine event delay-time distributions at different metallicities from the Binary Population and Spectral Synthesis (BPASS) models with an analytic model of the volume-averaged cosmic star formation rate density and chemical evolution to determine the volume-averaged rates of each event rate at the current time. We estimate rates in excellent agreement with extant observational constraints on core-collapse supernovae, thermonuclear supernovae and long GRBs. We predict rates for gravitational wave mergers based on the same stellar populations, and find rates consistent with current LIGO estimates. We note that tighter constraints on the rates of these events will be required before it is possible to determine their redshift evolution, progenitor metallicity dependence or constrain uncertain aspects of stellar evolution.

[228] arXiv:1807.07658v1 [pdf, vox]

Deriving star cluster parameters by convolutional neural networks. I. Age, mass, and size

J. Bialopetravičius, D. Narbutis, V. Vansevičius
Submitted Thursday 19 July 2018 @ 22:50:41 GMT
10 pages, 11 figures

Context. Convolutional neural networks (CNNs) are proven to perform fast classification and detection on natural images and have potential to infer astrophysical parameters on the exponentially increasing amount of sky survey imaging data. The inference pipeline can be trained either from real human-annotated data or simulated mock observations. Up to now star cluster analysis was based on integral or individual resolved stellar photometry. This limits the amount of information that can be extracted from cluster images. Aims. Develop a CNN based algorithm aimed to simultaneously derive ages, masses, and sizes of star clusters directly from multi-band images. Demonstrate CNN capabilities on low mass semi-resolved star clusters in a low signal-to-noise regime. Methods. A CNN was constructed based on the deep residual network (ResNet) architecture and trained on simulated images of star clusters with various ages, masses, and sizes. To provide realistic backgrounds, M31 star fields taken from the PHAT survey were added to the mock cluster images. Results. The proposed CNN was verified on mock images of artificial clusters and has demonstrated high precision and no significant bias for clusters of ages $\lesssim$3Gyr and masses between 250 and 4,000 ${\rm M_\odot}$. The pipeline is end-to-end starting from input images all the way to the inferred parameters, no hand-coded steps have to be performed - estimates of parameters are provided by the neural network in one inferential step from raw images.

[229] arXiv:1807.07654v1 [pdf, vox]

Inflation in Multi-field Modified DBM Potentials

Sonia Paban, Robert Rosati
Submitted Thursday 19 July 2018 @ 22:19:09 GMT
34 pages, 21 figures

We study multi-field inflation in random potentials generated via a non-equilibrium random matrix theory process. We make a novel modification of the process to include correlations between the elements of the Hessian and the height of the potential, similar to a Random Gaussian Field (RGF). We present the results of over 50,000 inflationary simulations involving 5-100 fields. For the first time, we present results of $\mathcal{O}(100)$ fields using the full `transport method', without slow-roll approximation. We conclude that Planck compatibility is a common prediction of such models, however significant isocurvature power at the end of inflation is possible.

[230] arXiv:1807.07641v1 [pdf, vox]

An X-ray view of central engines of low luminosity quasars (LLQSO) in the local Universe

Sibasish Laha, Ritesh Ghosh, Matteo Guainazzi, Alex G. Markowitz
Submitted Thursday 19 July 2018 @ 21:06:12 GMT
Published in the MNRAS journal

We have carried out a systematic X-ray spectral analysis of a sample of low luminosity quasars (LLQSO) to investigate the nature of the central engines of these sources. The optically-selected LLQSO sample consists of close, known bright active galactic nuclei (AGN) which serves as an important link between the powerful quasars at higher redshift and local Seyfert galaxies. We find that although the bolometric luminosities of the LLQSOs are lower than those of the higher redshift quasars by almost an order of magnitude, their distribution of the Eddington rate $\lambda_{\rm Edd}$ is similar. We detect a strong anti-correlation between $\alpha_{\rm OX}$ and $L_{2500 \rm \AA}$, as has also been detected in several other quasar studies with large sample sizes, indicating that as the UV luminosity of the source increases, the X-ray luminosity decreases. We do not detect any significant neutral obscuration ($N_{\rm H} \ge10^{22}\, \rm cm^{-2}$) in the X-ray spectra of the LLQSOs, and hence rule out obscuration as a possible cause for their lower luminosity. We conclude that the central engines of the LLQSOs function similarly to those of the higher redshift quasars, and the difference is possibly because of the fact that the LLQSOs have lower black hole masses. We do not find any correlation between the molecular gas in the host galaxies and accretion states of the AGN. This indicates that the presence of molecular gas in the host galaxies of the LLQSOs does not significantly influence the instantaneous accretion rates of their SMBHs.

[231] arXiv:1807.07625v1 [pdf, vox]

A comprehensive comparison between APOGEE and LAMOST: Radial Velocities and Atmospheric Stellar Parameters

B. Anguiano, S. R. Majewski, C. Allende-Prieto, S. Meszaros, H. Jönsson, D. A. García-Hernández, R. L. Beaton, G. S. Stringfellow, K. Cunha, V. V. Smith
Submitted Thursday 19 July 2018 @ 20:00:02 GMT
14 pages, 20 figures. Accepted for publication in Astronomy & Astrophysics (A&A)

We undertake a critical and comprehensive comparison of the radial velocities and the main stellar atmospheric parameters for stars in common between the latest data releases from the APOGEE and the LAMOST surveys. There is a total of 42,420 dwarfs/giants stars in common between the APOGEE DR14 - LAMOST DR3 stellar catalogs. A comparison between the RVs shows an offset of 4.54 $\pm$ 0.03 km/s, with a dispersion of 5.8 km/s, in the sense that APOGEE RVs are larger. We observe a small offset in the Teff of about 13 K, with a scatter of 155 K. Small offset in [Fe/H] of about 0.06 dex together with a scatter of 0.13 dex is also observed. We notice that the largest offset between the surveys occurs in the surface gravities. Using only surface gravities in calibrated red giants from APOGEE DR14, where there are 24,074 stars in common, a deviation of 0.14 dex is found with substantial scatter. There are 17,482 red giant stars in common between APOGEE DR14 and those in LAMOST tied to APOGEE DR12 via the Cannon. There is generally good agreement between the two data-sets. However, we find dependencies of the differences of the stellar parameters on effective temperature. For metal-rich stars, a different trend for the [Fe/H] discrepancies is found. Surprisingly, we see no correlation between the internal APOGEE DR14 - DR12 differences in Teff and those in DR14 - LAMOST tied to DR12, where a correlation should be expected since LAMOST has been calibrated to APOGEE DR12. We also find no correlation between the [Fe/H] discrepancies, suggesting that LAMOST/Cannon is not well coupled to the APOGEE DR12 stellar parameters scale. A [Fe/H] dependence between the stellar parameters in APOGEE DR12 and those in DR14 is reported. We find a weak correlation in the differences between APOGEE DR14 - DR12 and LAMOST on DR12 surface gravity for stars hotter than 4800 K and in the log g range between 2.0 and 2.8.

[232] arXiv:1807.07618v1 [pdf, vox]

IC4499 revised: spectro-photometric evidence of small light-element variations

E. Dalessandro, C. Lardo, M. Cadelano, S. Saracino, N. Bastian, A. Mucciarelli, M. Salaris, P. Stetson, E. Pancino
Submitted Thursday 19 July 2018 @ 19:33:52 GMT
9 pages, 9 figures, 3 tables; Accepted for publication in A&A

It has been suggested that IC4499 is one of the very few old globulars to not host multiple populations with light-element variations. To follow-up on this very interesting result, here we make use of accurate HST photometry and FLAMES@VLT high-resolution spectroscopy to investigate in more detail the stellar population properties of this system. We find that the red giant branch of the cluster is clearly bimodal in near-UV -- optical colour-magnitude diagrams, thus suggesting that IC4499 is actually composed by two sub-populations of stars with different nitrogen abundances. This represents the first detection of multiple populations in IC4499. Consistently, we also find that one star out of six is Na-rich to some extent, while we do not detect any evidence of intrinsic spread in both Mg and O. The number ratio between stars with normal and enriched nitrogen is in good agreement with the number ratio - mass trend observed in Galactic globular clusters. Also, as typically found in other systems, nitrogen rich stars are more centrally concentrated than normal stars, although this result cannot be considered conclusive because of the limited field of view covered by our observations (~$1r_h$). On the contrary, we observe that both the RGB UV color spread, which is a proxy of N variations, and Na abundance variations, are significantly smaller than those observed in Milky Way globular clusters with mass and metallicity comparable to IC4499. The modest N and Na spreads observed in this system can be tentatively connected to the fact that IC4499 likely formed in a disrupted dwarf galaxy orbiting the Milky Way, as previously proposed based on its orbit.

[233] arXiv:1807.07609v1 [pdf, vox]

Atmospheric Escape and the Evolution of Close-in Exoplanets

James E. Owen
Submitted Thursday 19 July 2018 @ 19:02:27 GMT
10,000 word review, submitted to Annual Reviews, comments welcome

Exoplanets with substantial Hydrogen/Helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels these atmospheres experience causes them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and lower-mass super-Earths/mini-Ne​ptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multi-dimensional calculations that incorporate magnetic-fields and interactions with the interstellar environment are cutting edge. However, there remains very limited comparison between simulations and observations. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower mass planets atmospheric escape drives and controls their evolution, sculpting the exoplanet population we observe today.

[234] arXiv:1807.07601v1 [pdf, vox]

The Extended Solar Cycle: Muddying the Waters of Solar/Stellar Dynamo Modeling Or Providing Crucial Observational Constraints?

A. K. Srivastava, S. W. McIntosh, N. Arge, D. Banerjee, E. Cliver, M. Dikpati, B. N. Dwivedi, M. Guhathakurta, B. B. Karak, R. J. Leamon, P. Martens, S. K. Matthew, A. Munoz-Jaramillo, D. Nandi, A. Norton, L. Upton, S. Chatterjee, R. Mazumder, Yamini K. Rao, R. Yadav
Submitted Thursday 19 July 2018 @ 18:42:12 GMT
11 Pages; 03 Figures

In 1844 Schwabe discovered that the number of sunspots increased and decreased over a period of about 11 years, that variation became known as the sunspot cycle. Almost eighty years later, Hale described the nature of the Sun's magnetic field, identifying that it takes about 22 years for the Sun's magnetic polarity to cycle. It was also identified that the latitudinal distribution of sunspots resembles the wings of a butterfly showing migration of sunspots in each hemisphere that abruptly start at mid-latitudes towards the Sun's equator over the next 11 years. These sunspot patterns were shown to be asymmetric across the equator. In intervening years, it was deduced that the Sun (and sun-like stars) possess magnetic activity cycles that are assumed to be the physical manifestation of a dynamo process that results from complex circulatory transport processes in the star's interior. Understanding the Sun's magnetism, its origin and its variation, has become a fundamental scientific objective \-- the distribution of magnetism, and its interaction with convective processes, drives various plasma processes in the outer atmosphere. In the past few decades, a range of diagnostic techniques have been employed to systematically study finer scale magnetized objects, and associated phenomena. The patterns discerned became known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC appeared to extend the wings of the activity butterfly back in time, nearly a decade before the formation of the sunspot pattern, and to much higher solar latitudes. In this short review, we describe their observational patterns of the ESC and discuss possible connections to the solar dynamo as we depart on a multi-national collaboration to investigate the origins of solar magnetism through a blend of archived and contemporary data analysis with the goal of improving solar dynamo understanding and modeling.

[235] arXiv:1807.07599v1 [pdf, vox]

Multiwavelength Light Curves of Two Remarkable Sagittarius A* Flares

G. G. Fazio, J. L. Hora, G. Witzel, S. P. Willner, M. L. N. Ashby, F. Baganoff, E. Becklin, S. Carey, D. Haggard, C. Gammie, A. Ghez, M. A. Gurwell, J. Ingalls, D. Marrone, M. R. Morris, H. A. Smith
Submitted Thursday 19 July 2018 @ 18:37:30 GMT
9 pages, 3 figures, to appear in the Astrophysical Journal

Sgr A*, the supermassive black hole (SMBH) at the center of our Milky Way Galaxy, is known to be a variable source of X-ray, near-infrared (NIR), and submillimeter (submm) radiation and therefore a prime candidate to study the electromagnetic radiation generated by mass accretion flow onto a black hole and/or a related jet. Disentangling the power source and emission mechanisms of this variability is a central challenge to our understanding of accretion flows around SMBHs. Simultaneous multiwavelength observations of the flux variations and their time correlations can play an important role in obtaining a better understanding of possible emission mechanisms and their origin. This paper presents observations of two flares that both apparently violate the previously established patterns in the relative timing of submm/NIR/X-ray flares from Sgr A*. One of these events provides the first evidence of coeval structure between NIR and submm flux increases, while the second event is the first example of the sequence of submm/X-ray/NIR flux increases all occurring within ~1 hr. Each of these two events appears to upend assumptions that have been the basis of some analytic models of flaring in Sgr A*. However, it cannot be ruled out that these events, even though unusual, were just coincidental. These observations demonstrate that we do not fully understand the origin of the multiwavelength variability of Sgr A*, and show that there is a continued and important need for long-term, coordinated, and precise multiwavelength observations of Sgr A* to characterize the full range of variability behavior.

[236] arXiv:1807.07594v1 [pdf, vox]

Emergence and Variability of Broad Absorption Line Quasar Outflows

Jesse A. Rogerson, Patrick B. Hall, Nabeel S. Ahmed, Paola Rodríguez Hidalgo, William N. Brandt, Nur Filiz Ak
Submitted Thursday 19 July 2018 @ 18:28:35 GMT
37 pages, 25 figures

We isolate a set of quasars that exhibit emergent C iv broad absorption lines (BALs) in their spectra by comparing spectra in the SDSS Data Release 7 and the SDSS/BOSS Data Releases 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. We find an emergence rate consistent with the previously reported disappearance rate of BAL quasars given the relative numbers of non-BAL and BAL quasars in the SDSS. We find candidate newly emerged BALs are preferentially drawn from among BALs with smaller balnicity indices, shallower depths, larger velocities, and smaller widths. Within two rest-frame years (average) after a BAL has emerged, we find it equally likely to continue increasing in equivalent width in an observation six months later (average) as it is to start decreasing. From the time separations between our observations, we conclude the coherence time-scale of BALs is less than 100 rest-frame days. We observe coordinated variability among pairs of troughs in the same quasar, likely due to clouds at different velocities responding to the same changes in ionizing flux; and the coordination is stronger if the velocity separation between the two troughs is smaller. We speculate the latter effect may be due to clouds having on average lower densities at higher velocities due to mass conservation in an accelerating flow, causing the absorbing gas in those clouds to respond on different timescales to the same ionizing flux variations.

[237] arXiv:1807.07585v1 [pdf, vox]

The supernova rate beyond the optical radius

Sukanya Chakrabarti, Brennan Dell, Or Graur, Alexei Filippenko, Benjamin Lewis, Christopher McKee
Submitted Thursday 19 July 2018 @ 18:01:19 GMT
accepted to Astrophysical Journal Letters

Many spiral galaxies have extended outer H~I disks and display low levels of star formation, inferred from the far-ultraviolet emission detected by {\it GALEX}, well beyond the optical radius. Here, we investigate the supernova (SN) rate in the outskirts of galaxies, using the largest and most homogeneous set of nearby supernovae (SNe) from the Lick Observatory Supernova Search (LOSS). While SN rates have been measured with respect to various galaxy properties, such as stellar mass and metallicity, their relative frequency in the outskirts versus the inner regions has not yet been studied. Understanding the SN rate as a function of intragalactic environment has many ramifications, including the interpretation of LIGO observations, the formation of massive stars, and the puzzlingly high velocity dispersion of the outer H~I disk. Using data from the LOSS survey, we find that the rate beyond the optical radius of spiral galaxies is $2.5 \pm 0.5$ SNe per millennium, while dwarf galaxies host $ 4.0 \pm 2.2$ SNe per millennium. The rates of core-collapse SNe (that may collapse to form the massive black holes detected by LIGO/Virgo) in the outer disks of spirals is $1.5 \pm 0.15$ SNe per millennium and in dwarf galaxies is $2.6 \pm 1.5$ SNe per millennium. Core-collapse SNe in spiral outskirts contribute $7600 \pm 1700$\,SNe\,~Gpc$^{-​3}$\,yr$^{-1}$ to the volumetric rate, and dwarf galaxies have a rate of $31,000 \pm 18,000$\,SNe\,Gpc$^{​-3}$\,yr$^{-1}$. The relative ratio of core-collapse to Type Ia SNe is comparable in the inner and outer parts of spirals, and in dwarf galaxies.

[238] arXiv:1807.07582v1 [pdf, vox]

Lithium abundance in lower red giant branch stars of Omega Centauri

A. Mucciarelli, M. Salaris, L. Monaco, P. Bonifacio, X. Fu, S. Villanova
Submitted Thursday 19 July 2018 @ 18:00:28 GMT
Accepted for publication in A&A, 10 pages, 9 figures, 2 tables

We present Li, Na, Al and Fe abundances of 199 lower red giant branch stars members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ~ 1 dex with a prominent tail toward lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ~ 1 dex are found at metallicities lower than [Fe/H] ~ -1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all the metallicities. The most metal-poor stars exhibit a clear Li-Na anticorrelation, with about 30% of the sample with A(Li) lower than ~ 0.8 dex, while in normal globular clusters these stars represent a small fraction. Most of the stars with [Fe/H] > -1.6 dex are Li-poor and Na-rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal​, Li-normal/Na-rich and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.

[239] arXiv:1807.07580v1 [pdf, vox]

Evolution of the galaxy stellar mass functions and UV luminosity functions at $z=6-9$ in the Hubble Frontier Fields

Rachana Bhatawdekar, Christopher Conselice, Berta Margalef-Bentabol, Kenneth Duncan
Submitted Thursday 19 July 2018 @ 18:00:11 GMT
25 Pages, 19 figures, Submitted to MNRAS

We present new measurements of the evolution of the galaxy stellar mass functions (GSMF) and UV luminosity functions (UV LF) for galaxies from $z=6-9$ within the Frontier Field cluster MACSJ0416.1-2403 and its parallel field. To obtain these results, we derive the stellar masses of our sample by fitting synthetic stellar population models to their observed spectral energy distribution with the inclusion of nebular emission lines. This is the deepest and farthest in distance mass function measured to date and probes down to a level of M$_{*} = 10^{6.8}M_{\odot}$. The main result of this study is that the low-mass end of our stellar mass functions to these limits and redshifts continues to become steeper from $-1.96_{-0.04}^{+0.0​4}$ at $z=6$ to $-2.38_{-0.25}^{+0.3​0}$ at $z=9$, steeper than previously observed, and we find no evidence of turnover in the mass range probed. We furthermore demonstrate that the UV LF for these system also continues to show a steepening at the highest redshifts, without any evidence of turnover in the luminosity range probed. Our $M_{\mathrm{UV}}-M_{​*}$ relation exhibit shallower slopes than previously observed and are in accordance with a constant mass-to-light ratio. Integrating our GSMF, we find that the stellar mass density increases by a factor of $\sim12$, from log$_{10}\rho_{*}=5.​63_{-0.89}^{+0.91}$ at $z=9$ to log$_{10}\rho_{*}=6.​74_{-0.12}^{+0.09}$ at $z=6$. We estimate the dust-corrected star formation rates (SFRs) to calculate the specific star formation rates ($\mathrm{sSFR}=\mat​hrm{SFR/M_{*}}$) of our sample, and find that for a fixed stellar mass of $5\times10^{9}M_{\od​ot}$, sSFR $\propto(1+z)^{2.01\​pm0.16}$. Finally, from our new measurements, we estimate the UV luminosity density ($\rho_{\textrm{UV}}​$) and find that our results support a smooth decline of $\rho_{\textrm{UV}}$ towards high redshifts.

[240] arXiv:1807.07579v1 [pdf, vox]

Exploring Fundamentally Three-dimensional Phenomena in High-fidelity Simulations of Core-collapse Supernovae

Evan O'Connor, Sean Couch
Submitted Thursday 19 July 2018 @ 18:00:06 GMT
20 pages, 14 figures, 0 explosions, submitted to The Astrophysical Journal. Comments welcome

The details of the physical mechanism that drives core-collapse supernovae (CCSNe) remain uncertain. While there is an emerging consensus on the qualitative outcome of detailed CCSN mechanism simulations in 2D, only recently have high-fidelity 3D simulations become possible. Here we present the results of an extensive set of 3D CCSN simulations using high-fidelity multidimensional neutrino transport, high-resolution hydrodynamics, and approximate general relativistic gravity. We employ a state-of-the-art 20 solar mass progenitor generated using the Modules for Experiments in Stellar Astrophysics (MESA; Farmer et al. (2016) Paxton et al. (2011, 2013, 2015, 2018) and the SFHo equation of state of Steiner et al. (2013). While none of our 3D CCSN simulations explode within ~500ms after core bounce, we find that the presence of large scale aspherical motion in the Si and O shells surrounding the collapsing iron core aid shock expansion and bring the models closer to the threshold of explosion. We also find some dependence on resolution and geometry (octant vs. full 4$\pi$). As has been noted in other recent works, we find that the post-shock turbulence plays an important role in determining the overall dynamical evolution of our simulations. We find a strong standing accretion shock instability (SASI) that develops at late times during the shock recession epoch. The SASI aids in transient shock expansion phases, but is not enough to result in shock revival. We also report that for a subset of our simulations, we find conclusive evidence for the LESA first reported in Tamborra et al. (2014), but until now, not confirmed by other simulation codes. Both the progenitor asphericities and the SASI-induced transient shock expansion phases generate transient gravitational waves and neutrino signal modulations via perturbations of the protoneutron star by turbulent motions. (abridged)

[241] arXiv:1807.07578v1 [pdf, vox]

Unrestored Electroweak Symmetry

Patrick Meade, Harikrishnan Ramani
Submitted Thursday 19 July 2018 @ 18:00:03 GMT
7 pages, 4 figures

The commonly assumed cosmological history of our universe is that at early-times and high-temperatures the universe went through an ElectroWeak Phase Transition (EWPT). Assuming an EWPT, and depending on its strength, there are many implications for baryogenesis, gravitational waves, and the evolution of the universe in general. However, it is not true that all spontaneously broken symmetries at zero-temperature are restored at high-temperature. In particular the idea of "inverse symmetry breaking" has long been established in scalar theories with evidence from both perturbative and lattice calculations. In this letter we demonstrate that with a simple extension of the SM it is possible that the ElectroWeak (EW) symmetry was always broken or only temporarily passed through a symmetry restored phase. These novel phase histories have many cosmological and collider implications that we discuss. The model presented here serves as a useful benchmark comparison for future attempts to discern the phase of our universe at $T\gtrsim$ a few GeV.

[242] arXiv:1807.07576v1 [pdf, vox]

Red vs Blue: Early observations of thermonuclear supernovae reveal two distinct populations?

Maximilian D. Stritzinger, Benjamin J. Shappee, Anthony L. Piro, Christopher Ashall, E. Baron, Peter Hoeflich, Simon Holmbo, Thomas W. -S. Holoien, M. M. Phillips, C. R. Burns, Carlos Contreras, Nidia Morrell, Michael A. Tucker
Submitted Thursday 19 July 2018 @ 18:00:02 GMT
Submitted to ApJ Letters on June 27, 7 pages, including 4 figures and 1 table. Constructive comments are most welcome

We examine the early phase intrinsic $(B-V)_{0}$ color evolution of a dozen Type~Ia supernovae discovered within three days of inferred time of first light ($t_{first}$) and have $(B-V)_0$ color information beginning within 5 days of $t_{first}$. The sample indicates there are two distinct early populations. The first is a population exhibiting blue colors that slowly evolve, and the second population exhibits red colors and evolves more rapidly. Placing the first sample on the Branch diagram (i.e., ratio of \ion{Si}{2} $\lambda\lambda$5972​, 6355 pseudo-Equivalent widths) indicates all blue objects are of the Branch Shallow Silicon (SS) spectral type, while all early-red events --except for the peculiar SN~2012fr-- are of the Branch Core-Normal (CN) or CooL (CL) type. Inspection of their light curves indicate early-blue events are typically more luminous with slower declining light curves than those exhibiting early-red colors.A number of potential processes contributing to the early emission are explored, and we caution that great care must be taken when interpreting early-phase light curves.

[243] arXiv:1807.07575v1 [pdf, vox]

The prevalence and properties of cold gas inflows and outflows around galaxies in the local Universe

G. W. Roberts-Borsani, A. Saintonge
Submitted Thursday 19 July 2018 @ 18:00:00 GMT
Submitted to MNRAS. 34 pages, 28 figures

We perform a stacking analysis of the neutral NaD$\lambda\lambda$5​889,5895\AA\ ISM doublet using the SDSS DR7 spectroscopic data set to probe the prevalence and characteristics of cold (T$\lesssim$10$^{4}$ K) galactic-scale flows in local (0.025$\leqslant z\leqslant$0.1) inactive and AGN-host galaxies across the SFR-M$_{*}$ plane. We find low-velocity outflows to be prevalent in regions of high SFRs and stellar masses (10 $\lesssim$log M$_{*}$/M$_{\odot}$ $\lesssim$ 11.5), however we do not find any detections in the low mass (log M$_{*}$/M$_{\odot}$ $\lesssim$ 10) regime. We also find tentative detections of inflowing gas in high mass galaxies across the star forming populations. We derive mass outflow rates with ranges 0.14-1.74\,M$_{\odot​}$yr$^{-1}$ and upper limits on inflow rates <2 M$_{\odot}$yr$^{-1}$​, allowing us to place constraints on the mass loading factor ($\eta$=$\dot{M}_{\t​ext{out}}$/SFR) for use in simulations of the local Universe. We discuss the fate of the outflows by comparing the force provided by the starburst to the critical force needed to push the outflow outward, and find the vast majority of the outflows unlikely to escape the host system. Finally, as outflow detection rates and central velocities do not vary strongly with the presence of a (weak) active supermassive black hole, we determine that star formation appears to be the primary driver of outflows at $z\sim$0.

[244] arXiv:1807.07900v1 [pdf, vox]

A Fourier Domain "Jerk" Search for Binary Pulsars

Bridget C. Andersen, Scott M. Ransom
Submitted Thursday 19 July 2018 @ 17:59:59 GMT
Submitted to ApJ Letters

While binary pulsar systems are fantastic laboratories for a wide array of astrophysics, they are particularly difficult to detect. The orbital motion of the pulsar changes its apparent spin frequency over the course of an observation, essentially "smearing" the response of the time series in the Fourier domain. We review the Fourier domain acceleration search (FDAS), which uses a matched filtering algorithm to correct for this smearing by assuming constant acceleration for a small enough portion of the orbit. We discuss the theory and implementation of a Fourier domain "jerk" search, developed as part of the \textsc{PRESTO} software package, which extends the FDAS to account for a linearly changing acceleration, or constant orbital jerk, of the pulsar. We test the performance of our algorithm on archival Green Bank Telescope observations of the globular cluster Terzan~5, and show that while the jerk search has a significantly longer runtime, it improves search sensitivity to binaries when the observation duration is $5$ to $15\%$ of the orbital period. Finally, we present the jerk-search-enabled detection of Ter5am (PSR~J1748$-$2446am)​, a new highly-accelerated pulsar in a compact, eccentric, and relativistic orbit, with a likely pulsar mass of 1.649$^{+0.037}_{-0.​11}$\,\msun.

[245] arXiv:1807.07557v1 [pdf, vox]

WASP-128b: a transiting brown dwarf in the dynamical-tide regime

V. Hodžić, A. H. M. J. Triaud, D. R. Anderson, F. Bouchy, A. Collier Cameron, L. Delrez, M. Gillon, C. Hellier, E. Jehin, M. Lendl, P. F. L. Maxted, F. Pepe, D. Pollacco, D. Queloz, D. Ségransan, B. Smalley, S. Udry, R. West
Submitted Thursday 19 July 2018 @ 17:55:08 GMT
7 pages, 3 figures. Submitted to MNRAS. Comments welcome

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a $2.2\,\mathrm{d}$ orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor $\log{Q_\star'} = 6.96 \pm 0.19$. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, $M_\star = 1.16 \pm 0.04\,M_\odot$, $R_\star = 1.16 \pm 0.02\,R_\odot$, and for the companion, $M_\mathrm{b} =37.5 \pm 0.8\,M_\mathrm{Jup}$​, $R_\mathrm{b} = 0.94 \pm 0.02\,R_\mathrm{Jup}​$, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters.

[246] arXiv:1807.05611v2 [pdf, vox]

The magnetosphere structure of a Kerr black hole: marginally force-free equatorial boundary condition

Zhen Pan
Submitted Thursday 19 July 2018 @ 17:03:27 GMT

The role of equatorial boundary condition in the structure of a force-free black hole magnetosphere was rarely discussed, since previous studies have been focused on the the field lines entering the horizon. However, recent high-accuracy force-free electrodynamics (FFE) simulations \cite{East2018} show that there are both field lines entering the horizon and field lines ending up on the equatorial current sheet within the ergosphere for asymptotic uniform field configuration. For the latter field lines, the equatorial boundary condition is well approximated being marginally force-free, i.e., $B^2-E^2\approx 0$, where $B$ and $E$ are the magnetic and electric field strength, respectively. In this paper, we revisit the uniform field solution to the Kerr BH magnetosphere structure and investigate the role of the marginally force-free equatorial boundary condition. We find this boundary condition plays an important role in shaping the BH magnetosphere in various aspects, including the shape of the light surface, the near-horizon field line configuration and the source of the Poynting flux. We also propose an algorithm for numerically solving the Grad-Shafranov equation and self-consistently imposing the marginally force-free equatorial condition. As a result, we find a good agreement between our numerical solutions and the high-accuracy FFE simulations. We also discuss the applicability of the marginally force-free boundary condition and the numerical algorithm proposed in this paper for general magnetic field configurations.

[247] arXiv:1807.06668v2 [pdf, vox]

NPF: mirror development in Chile

Sebastián Zúñiga-Fernández, Amelia Bayo, Johan Olofsson, Leslie Pedrero, Claudio Lobos, Elias Rozas, Nicolás Soto, Matthias Schreiber, Pedro Escárate, Christian Romero, Hayk Hakobyan, Jorge Cuadra, Cristopher Rozas, John D. Monnier, Stefan Kraus, Mike J. Ireland, Pedro Mardones
Submitted Thursday 19 July 2018 @ 15:42:01 GMT
13 pages, SPIE Proceedings Volume 10700, Ground-based and Airborne Telescopes VII; 107003X (2018). Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

In the era of high-angular resolution astronomical instrumentation, where long and very long baseline interferometers (constituted by many, $\sim$ 20 or more, telescopes) are expected to work not only in the millimeter and submillimeter domain, but also at near and mid infrared wavelengths (experiments such as the Planet Formation Imager, PFI, see Monnier et al. 2018 for an update on its design); any promising strategy to alleviate the costs of the individual telescopes involved needs to be explored. In a recent collaboration between engineers, experimental physicists and astronomers in Valparaiso, Chile, we are gaining expertise in the production of light carbon fiber polymer reinforced mirrors. The working principle consists in replicating a glass, or other substrate, mandrel surface with the mirrored adequate curvature, surface characteristics and general shape. Once the carbon fiber base has hardened, previous studies have shown that it can be coated (aluminum) using standard coating processes/techniques designed for glass-based mirrors. The resulting surface quality is highly dependent on the temperature and humidity control among other variables. Current efforts are focused on improving the smoothness of the resulting surfaces to meet near/mid infrared specifications, overcoming, among others, possible deteriorations derived from the replication process. In a second step, at the validation and quality control stage, the mirrors are characterized using simple/traditional tools like spherometers (down to micron precision), but also an optical bench with a Shack-Hartman wavefront sensor. This research line is developed in parallel with a more classical glass-based approach, and in both cases we are prototyping at the small scale of few tens of cms. We here present our progress on these two approaches.

[248] arXiv:1807.07496v1 [pdf, vox]

Advanced ACTPol TES Device Parameters and Noise Performance in Fielded Arrays

Kevin T. Crowley, Jason E. Austermann, Steve K. Choi, Shannon M. Duff, Patricio A. Gallardo, Shuay-Pwu Patty Ho, Johannes Hubmayr, Brian J. Koopman, Federico Nati, Michael D. Niemack, Maria Salatino, Sara M. Simon, Suzanne T. Staggs, Jason R. Stevens, Joel N. Ullom, Eve M. Vavagiakis, Edward J. Wollack
Submitted Thursday 19 July 2018 @ 15:34:39 GMT
Accepted for publication in Journal of Low Temperature Physics for LTD-17 special issue

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT) features arrays of aluminum manganese transition-edge sensors (TESes) optimized for ground-based observations of the Cosmic Microwave Background (CMB). Array testing shows highly responsive detectors with anticipated in-band noise performance under optical loading. We report on TES parameters measured with impedance data taken on a subset of TESes. We then compare modeled noise spectral densities to measurements. We find excess noise at frequencies around 100 Hz, nearly outside of the signal band of CMB measurements. In addition, we describe full-array noise measurements in the laboratory and in the field for two new AdvACT mid-frequency arrays, sensitive at bands centered on 90 and 150 GHz, and data for the high-frequency array (150/230 GHz) as deployed.

[249] arXiv:1807.07494v1 [pdf, vox]

Back-Reaction of Super-Hubble Cosmological Perturbations Beyond Perturbation Theory

Robert Brandenberger, Leila L. Graef, Giovanni Marozzi, Gian Paolo Vacca
Submitted Thursday 19 July 2018 @ 15:30:04 GMT
9 pages

We discuss the effect of super-Hubble cosmological fluctuations on the locally measured Hubble expansion rate. We consider a large bare cosmological constant in the early universe in the presence of scalar field matter (the dominant matter component), which would lead to a scale-invariant primordial spectrum of cosmological fluctuations. Using the leading order gradient expansion we show that the expansion rate measured by a (secondary) clock field which is not comoving with the dominant matter component obtains a negative contribution from infrared fluctuations, a contribution whose absolute value increases in time. This is the same effect which a decreasing cosmological constant would produce. This supports the conclusion that infrared fluctuations lead to a dynamical relaxation of the cosmological constant. Our analysis does not make use of any perturbative expansion in the amplitude of the inhomogeneities.

[250] arXiv:1807.07493v1 [pdf, vox]

The Carnegie RR Lyrae Program: Mid-infrared Period-Luminosity relations of RR Lyrae stars in Reticulum

Tatiana Muraveva, Alessia Garofalo, Victoria Scowcroft, Gisella Clementini, Wendy L. Freedman, Barry F. Madore, Andrew J. Monson
Submitted Thursday 19 July 2018 @ 15:29:46 GMT
17 pages, 10 figures. Accepted for publication in MNRAS

We analysed 30 RR Lyrae stars (RRLs) located in the Large Magellanic Cloud (LMC) globular cluster Reticulum that were observed in the 3.6 and 4.5 $\mu$m passbands with the Infrared Array Camera (IRAC) on board of the Spitzer Space Telescope. We derived new mid-infrared (MIR) period-luminosity PL relations. The zero points of the PL relations were estimated using the trigonometric parallaxes of five bright Milky Way (MW) RRLs measured with the Hubble Space Telescope (HST) and, as an alternative, we used the trigonometric parallaxes published in the first Gaia data release (DR1) which were obtained as part of the Tycho-Gaia Astrometric Solution (TGAS) and the parallaxes of the same stars released with the second Gaia data release (DR2). We determined the distance to Reticulum using our new MIR PL relations and found that distances calibrated on the TGAS and DR2 parallaxes are in a good agreement and, generally, smaller than distances based on the HST parallaxes, although they are still consistent within the respective errors. We conclude that Reticulum is located ~3 kpc closer to us than the barycentre of the LMC.

[251] arXiv:1807.07479v1 [pdf, vox]

Statistics of Photospheric Supergranular Cells Observed by SDO/HMI

Majedeh Noori, Mohsen Javaherian, Hossein Safari, Hamid Nadjari
Submitted Thursday 19 July 2018 @ 15:03:29 GMT
13 pages, 9 figures

Aims: The statistics of the photospheric granulation pattern are investigated using continuum images observed by Solar Dynamic Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) taken at 6713~\AA. Methods: The supergranular boundaries can be extracted by tracking photospheric velocity plasma flows. The local ball-tracking method is employed to apply on the HMI data gathered over the years 2011-2015 to estimate the boundaries of the cells. The edge sharpening techniques are exerted on the output of ball-tracking to precisely identify the cells borders. To study the fractal dimensionality (FD) of supergranulation, the box counting method is used. Results: We found that both the size and eccentricity follow the log-normal distributions with peak values about 330 Mm$^2$ and 0.85, respectively. The five-year mean value of the cells number appeared in half-hour sequences is obtained to be about 60 $\pm$ 6 within an area of $350^{\prime\prime}\​times350^{\prime\pri​me}$. The cells orientation distribution presents the power-law behavior. Conclusions: The orientation of supergranular cells ($O$) and their size ($S$) follows a power-law function as $|O| \propto S^{9.5}$. We found that the non-roundish cells with smaller and larger sizes than 600 Mm$^2$ are aligned and perpendicular with the solar rotational velocity on the photosphere, respectively. The FD analysis shows that the supergranular cells form the self-similar patterns.

[252] arXiv:1807.07467v1 [pdf, vox]

Hi-5: a potential high-contrast thermal near-infrared imager for the VLTI

D. Defrère, M. Ireland, O. Absil, J. -P. Berger, W. C. Danchi, S. Ertel, A. Gallenne, F. Hénault, P. Hinz, E. Huby, S. Kraus, L. Labadie, J. -B. Le Bouquin, G. Martin, A. Matter, B. Mennesson, A. Mérand, S. Minardi, J. D. Monnier, B. Norris, G. Orban de Xivry, E. Pedretti, J. -U. Pott, M. Reggiani, E. Serabyn, J. Surdej, K. R. W. Tristram, J. Woillez
Submitted Thursday 19 July 2018 @ 14:41:16 GMT
15 pages, 3 figures, SPIE proceedings, based on arXiv:1801.04148

Hi-5 is a high-contrast (or high dynamic range) infrared imager project for the VLTI. Its main goal is to characterize young extra-solar planetary systems and exozodiacal dust around southern main-sequence stars. In this paper, we present an update of the project and key technology pathways to improve the contrast achieved by the VLTI. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5~$\mu$m) and advanced fringe tracking strategies. We also address the strong exoplanet science case (young exoplanets, planet formation, and exozodiacal disks) offered by this wavelength regime as well as other possible science cases such as stellar physics (fundamental parameters and multiplicity) and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed.

[253] arXiv:1807.07462v1 [pdf, vox]

Mid-infrared variability of the neutrino source blazar TXS 0506$+$056

K. É. Gabányi, A. Moór, S. Frey
Submitted Thursday 19 July 2018 @ 14:33:50 GMT
3 pages, 1 figure; accepted by the Research Notes of the American Astronomical Society

The IceCube instrument detected a high-energy cosmic neutrino event on 2017 September 22 (IceCube_170922A, IceCube Collaboration 2018), which the electromagnetic follow-up campaigns associated with the flaring $\gamma$-ray blazar TXS 0506$+$056 (e.g., Padovani et al., 2018). We investigated the mid-infrared variability of the source by using the available single exposure data of the WISE satellite at $3.4$ and $4.6\mu$m. TXS 0506$+$056 experienced a $\sim 30$% brightening in both of these bands a few days prior to the neutrino event. Additional intraday infrared variability can be detected in 2010. Similar behaviour seen previously in $\gamma$-ray bright radio-loud AGN has been explained by their jet emission (e.g., Jiang et al. 2012).

[254] arXiv:1807.07456v1 [pdf, vox]

An atlas of cool supergiants from the Magellanic Clouds and typical interlopers: Atlas of cool supergiants in the Magellanic Clouds

Ricardo Dorda, Ignacio Negueruela, Carlos González-Fernández, Amparo Marco
Submitted Thursday 19 July 2018 @ 14:16:02 GMT
Accepted for publication in A&A. The atlas of spectra and the complete list of targets will be available at CDS, once the paper is published

We present an atlas composed of more than 1500 spectra of late-type stars (spectral types from G to M) observed simultaneously in the optical and calcium triplet spectral ranges. These spectra were obtained as part of a survey to search for cool supergiants in the Magellanic Clouds and were taken over four epochs. We provide the spectral and luminosity classification for each spectrum (71% are supergiants, 13% are giants or luminous giants, 4% are carbon or S stars, and the remaining 12% are foreground stars of lesser luminosities). We also provide a detailed guide for the spectral classification of luminous late-type stars, the result of the extensive classification work done for the atlas. Although this guide is based on classical criteria, we have put them together and re-elaborated them for modern CCD-spectra as these criteria were scattered among many different works and mainly conceived for use with photographic plate spectra. The result is a systematic, well-tested process for identifying and classifying luminous late-type stars, illustrated with CCD spectra of standard stars and the classifications of our own catalogue.

[255] arXiv:1807.07402v1 [pdf, vox]

The MICADO first light imager for ELT: its astrometric performance

J. -U. Pott, G. Rodeghiero, H. Riechert, D. Massari, M. Fabricius, C. Arcidiacono, R. I. Davies
Submitted Thursday 19 July 2018 @ 13:35:49 GMT
5 pages, submitted to SPIE 2018 Astronomical Telescopes + Instrumentation

We report on our ongoing efforts to ensure that the MICADO NIR imager reaches differential absolute (often abbreviated: relative) astrometric performance limited by the SNR of typical observations. The exceptional 39m diameter collecting area in combination with a powerful multi-conjugate adaptive optics system (called MAORY) brings the nominal centroiding error, which scales as FWHM/SNR, down to a few 10 uas. Here we show that an exceptional effort is needed to provide a system which delivers adequate and calibrateable astrometric performance over the full field of view (up to 53 arcsec diameter).

[256] arXiv:1807.07375v1 [pdf, vox]

The $γ$-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT

H. E. S. S. Collaboration, H. Abdalla, A. Abramowski, F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, C. Armand, M. Arrieta, M. Backes, A. Balzer, M. Barnard, Y. Becherini, J. Becker Tjus, D. Berge, S. Bernhard, K. Bernlöhr, R. Blackwell, M. Böttcher, C. Boisson, J. Bolmont, S. Bonnefoy, P. Bordas, J. Bregeon, F. Brun, P. Brun, M. Bryan, M. Büchele, T. Bulik, M. Capasso, S. Caroff, A. Carosi, S. Casanova, M. Cerruti, N. Chakraborty, R. C. G. Chaves, A. Chen, J. Chevalier, S. Colafrancesco, B. Condon, J. Conrad, I. D. Davids, J. Decock, C. Deil, J. Devin, P. deWilt, L. Dirson, A. Djannati-Ataï, A. Donath, L. O'C. Drury, J. Dyks, T. Edwards, K. Egberts, G. Emery, J. -P. Ernenwein, S. Eschbach, C. Farnier, S. Fegan, M. V. Fernandes, A. Fiasson, G. Fontaine, S. Funk, M. Füßling, S. Gabici, Y. A. Gallant, T. Garrigoux, F. Gaté, G. Giavitto, D. Glawion, J. F. Glicenstein, D. Gottschall, M. -H. Grondin, J. Hahn, M. Haupt, J. Hawkes, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, C. Hoischen, T. L. Holch, M. Holler, D. Horns, A. Ivascenko, H. Iwasaki, A. Jacholkowska, M. Jamrozy, D. Jankowsky, F. Jankowsky, M. Jingo, L. Jouvin, I. Jung-Richardt, M. A. Kastendieck, K. Katarzyński, M. Katsuragawa, U. Katz, D. Kerszberg, D. Khangulyan, B. Khélifi, J. King, S. Klepser, D. Klochkov, W. Kluźniak, Nu. Komin, K. Kosack, S. Krakau, M. Kraus, P. P. Krüger, H. Laffon, G. Lamanna, J. Lau, J. Lefaucheur, A. Lemière, M. Lemoine-Goumard, J. -P. Lenain, E. Leser, T. Lohse, M. Lorentz, R. Liu, R. López-Coto, I. Lypova, D. Malyshev, V. Marandon, A. Marcowith, C. Mariaud, R. Marx, G. Maurin, N. Maxted, M. Mayer, P. J. Meintjes, M. Meyer, A. M. W. Mitchell, R. Moderski, M. Mohamed, L. Mohrmann, K. Morå, E. Moulin, T. Murach, S. Nakashima, M. de Naurois, H. Ndiyavala, F. Niederwanger, J. Niemiec, L. Oakes, P. O'Brien, H. Odaka, S. Ohm, M. Ostrowski, I. Oya, M. Padovani, M. Panter, R. D. Parsons, N. W. Pekeur, G. Pelletier, C. Perennes, P. -O. Petrucci, B. Peyaud, Q. Piel, S. Pita, V. Poireau, D. A. Prokhorov, H. Prokoph, G. Pühlhofer, M. Punch, A. Quirrenbach, S. Raab, R. Rauth, A. Reimer, O. Reimer, M. Renaud, R. de los Reyes, F. Rieger, L. Rinchiuso, C. Romoli, G. Rowell, B. Rudak, C. B. Rulten, V. Sahakian, S. Saito, D. A. Sanchez, A. Santangelo, M. Sasaki, R. Schlickeiser, F. Schüssler, A. Schulz, U. Schwanke, S. Schwemmer, M. Seglar-Arroyo, A. S. Seyffert, N. Shafi, I. Shilon, K. Shiningayamwe. R. Simoni, H. Sol, F. Spanier, M. Spir-Jacob, Ł. Stawarz, R. Steenkamp, C. Stegmann, C. Steppa, I. Sushch, T. Takahashi, J. -P. Tavernet, T. Tavernier, A. M. Taylor, R. Terrier, L. Tibaldo, D. Tiziani, M. Tluczykont, C. Trichard, M. Tsirou, N. Tsuji, R. Tuffs, Y. Uchiyama, D. J. van der Walt, C. van Eldik, C. van Rensburg, B. van Soelen, G. Vasileiadis, J. Veh, C. Venter, A. Viana, P. Vincent, J. Vink, F. Voisin, H. J. Völk, T. Vuillaume, Z. Wadiasingh, S. J. Wagner, P. Wagner, R. M. Wagner, R. White, A. Wierzcholska, P. Willmann, A. Wörnlein, D. Wouters, R. Yang, D. Zaborov, M. Zacharias, R. Zanin, A. A. Zdziarski, A. Zech, F. Zefi, A. Ziegler, J. Zorn, N. Żywucka, Fermi-LAT collaboration, J. D. Magill, S. Buson, C. C. Cheung, J. S. Perkins, Y. Tanaka
Submitted Thursday 19 July 2018 @ 12:54:51 GMT
Accepted for publication in A&A, Abstract abridged for arXiv submission

Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV-100 TeV) $\gamma$-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE $\gamma$-ray emitter, though its VHE flux exceeds both the extrapolation from early Fermi-LAT observations as well as expectations from a (misaligned) single-zone synchrotron-self Compton (SSC) description. The latter satisfactorily reproduces the emission from Cen A at lower energies up to a few GeV. New observations with H.E.S.S., comparable in exposure time to those previously reported, were performed and eight years of Fermi-LAT data were accumulated to clarify the spectral characteristics of the $\gamma$-ray emission from the core of Cen A. The results allow us for the first time to achieve the goal of constructing a representative, contemporaneous $\gamma$-ray core spectrum of Cen A over almost five orders of magnitude in energy. Advanced analysis methods, including the template fitting method, allow detection in the VHE range of the core with a statistical significance of 12$\sigma$ on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV-6 TeV is compatible with a power-law function with a photon index $\Gamma=2.52\pm0.13_​{\mathrm{stat}}\pm0.​20_{\mathrm{sys}}$. An updated Fermi-LAT analysis provides evidence for spectral hardening by $\Delta\Gamma\simeq0​.4\pm0.1$ at $\gamma$-ray energies above $2.8^{+1.0}_{-0.6}$ GeV at a level of $4.0\sigma$. The fact that the spectrum hardens at GeV energies and extends into the VHE regime disfavour a single-zone SSC interpretation for the overall spectral energy distribution (SED) of the core and is suggestive of a new $\gamma$-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies.

[257] arXiv:1807.07568v1 [pdf, vox]

Unravelling the progenitors of merging black hole binaries

Nicola Giacobbo, Michela Mapelli, Mario Spera
Submitted Thursday 19 July 2018 @ 12:32:52 GMT
6 pages, 3 figures; to appear in Proceeding of Science; proceeding of the GRAvitational-waves Science & technology Symposium - GRASS2018, 1-2 March 2018, Palazzo Moroni, Padova (Italy)

The recent detection of gravitational waves has proven the existence of massive stellar black hole binaries (BBHs), but the formation channels of BBHs are still an open question. Here, we investigate the demography of BBHs by using our new population-synthesis code MOBSE. MOBSE is an updated version of the widely used binary population-synthesis code BSE (Hurley et al. 2000, Hurley et al. 2002) and includes the key ingredients to determine the fate of massive stars: up-to-date stellar wind prescriptions and supernova models. With MOBSE, we form BBHs with total mass up to $\sim{}120$ M$_\odot$ at low metallicity, but only systems with total mass up to $\sim{}80$ M$_\odot$ merge in less than a Hubble time. Our results show that only massive metal-poor stars ($Z\lesssim 0.002$) can be the progenitors of gravitational wave events like GW150914. Moreover, we predict that merging BBHs form much more efficiently from metal-poor than from metal-rich stars.

[258] arXiv:1807.07359v1 [pdf, vox]

UVIT imaging of WLM : Demographics of star forming regions in the nearby dwarf irregular galaxy

Chayan Mondal, Annapurni Subramaniam, Koshy George
Submitted Thursday 19 July 2018 @ 12:13:23 GMT
Accepted for publication in AJ

We present a study of star forming regions and its demographics in the nearby dwarf irregular galaxy WLM using the Ultra-Violet Imaging Telescope (UVIT) multi band observations in three filters F148W, N245M and N263M. We find that the UV emission is extended at least up to 1.7 kpc, with the NUV emission more extended than the FUV. We create UV color maps ((F148W$-$N245M) and (F148W$-$N263M)) to study the temperature morphology of young stellar complexes with the help of theoretical models. We identify several complexes with temperature T $>$ 17500 K which are likely to be the OB associations present in the galaxy. These complexes show good spatial correlation with the H$\alpha$ emitting regions, H$~$I distribution and HST detected hot stars. The hot star forming regions are found to be clumpy in nature and show a hierarchical structure, with sizes in the range of 4 - 50 pc, with a large number with sizes $<$ 10 pc. The south western part of the galaxy shows many hot star forming regions, high level of H$\alpha$ emission and low column density of H$~$I which altogether denote a vigorous recent star formation. WLM is likely to have a large fraction of low mass compact star forming regions with mass M $< 10^3 M_{\odot}$, in agreement with the size and mass of the CO clouds. We estimate the star formation rate of WLM to be $\sim$ 0.008 $M_{\odot}/yr$, which is similar to the average value measured for nearby dwarf irregular galaxies.

[259] arXiv:1807.06232v2 [pdf, vox]

FOREST Unbiased Galactic Plane Imaging Survey with the Nobeyama 45-m Telescope (FUGIN) IV: Galactic Shock Wave and Molecular Bow Shock in the 4-kpc Arm of the Galaxy

Y. Sofue, M. Kohno, K. Torii, T. Umemoto, N. Kuno, K. Tachihara, T. Minamidani, S. Fujita, M. Matsuo, A. Nishimura, Y. Tsuda, M. Seta
Submitted Thursday 19 July 2018 @ 11:44:06 GMT
13 pages, 11 figures, 1 table, PASJ in press (2019 special issue for NRO-45m Telescope FOREST project)

The FUGIN CO survey with the Nobeyama 45-m Telescope revealed the 3D structure of a galactic shock wave in the tangential direction of the 4-kpc molecular arm. The shock front is located at G30.5+00.0+95 km/s on the up-stream (lower longitude) side of the star-forming complex W43 (G30.8-0.03), and composes a molecular bow shock (MBS) concave to W43, exhibiting an arc-shaped molecular ridge perpendicular to the galactic plane with width $\sim 0^\circ.1$ (10 pc) and vertical length $\sim 1^\circ \ (100\ {\rm pc})$. The MBS is coincident with the radio continuum bow of thermal origin, indicating association of ionized gas and similarity to a cometary bright-rimmed cloud. The up-stream edge of the bow is sharp with a growth width of $\sim 0.5$ pc indicative of shock front property. The velocity width is $\sim 10$ km/s, and the center velocity decreases by $\sim 15$ \kms from bottom to top of the bow. The total mass of molecular gas in MBS is estimated to be $\sim 1.2\times 10^6 <_\odot$ and ionized gas $\sim 2\times 10^4 M_\odot$. The vertical disk thickness increases step like at the MBS by $\sim 2$ times from lower to upper longitude, which indicates hydraulic-jump in the gaseous disk. We argue that the MBS was formed by the galactic shock compression of an accelerated flow in the spiral-arm potential encountering the W43 molecular complex. A bow-shock theory can well reproduce the bow morphology. We argue that molecular bows are common in galactic shock waves not only in the Galaxy but also in galaxies, where MBS are associated with giant cometary HII regions. We also analyzed the HI data in the same region to obtain a map of HI optical depth and molecular fraction. We found a firm evidence of HI-to-H$_{2}$ transition in the galactic shock as revealed by a sharp molecular front at the MBS front.

[260] arXiv:1807.07334v1 [pdf, vox]

Giant burst of methanol maser in S255IR-NIRS3

Marian Szymczak, Mateusz Olech, Paweł Wolak, Eric Gérard, Anna Bartkiewicz
Submitted Thursday 19 July 2018 @ 10:33:24 GMT
9 pages, 9 figures

Context: High-mass young stellar objects (HMYSOs) can undergo accretion episodes that strongly affect the star evolution, the dynamics of the disk, and its chemical evolution. Recently reported extraordinary bursts in the methanol maser emission may be the observational signature of accretion events in deeply embedded HMYSOs. Aims: We analyze the light curve of 6.7 GHz methanol masers in S255IR-NIRS3 during the 2015-2016 burst. Methods: 8.5-year monitoring data with an average sampling interval of 5 days were obtained with the Torun 32 m radio telescope. Archival data were added, extending the time series to ~27 years. Results: The maser emission showed moderate (25-30%) variability on timescales of months to years over ~23 years since its discovery. The main burst was preceded by a one-year increase of the total flux density by a factor of 2.5, then it grew by a factor of 10 over ~0.4 years and declined by a factor of 8 during the consecutive 2.4 years. The peak maser luminosity was a factor of 24.5 higher than the pre-burst quiescent value. The light curves of individual features showed considerable diversity but indicated a general trend of suppression of the maser emission at blueshifted (<4.7 km s$^{-1}$) velocities when the redshifted emission rapidly grew and new emission features appeared at velocities >5.8 km s$^{-1}$. This new emission provided a contribution of about 80% to the maser luminosity around the peak of the burst. Conclusions: The onset of the maser burst exactly coincides with that of the infrared burst estimated from the motion of the light echo. This strongly supports the radiative pumping scheme of the maser transition. The growth of the maser luminosity is the result of an increasing volume of gas where the maser inversion is achieved.

[261] arXiv:1807.07324v1 [pdf, vox]

Foreground Biases on Primordial Non-Gaussianity Measurements from the CMB Temperature Bispectrum: Implications for Planck and Beyond

J. Colin Hill
Submitted Thursday 19 July 2018 @ 10:01:45 GMT
18 pages, 10 figures, abstract slightly abridged, comments welcome

The cosmic microwave background (CMB) temperature bispectrum is currently the most precise tool for constraining primordial non-Gaussianity (NG). The Planck temperature data tightly constrain the amplitude of local-type NG: $f_{\rm NL}^{\rm loc} = 2.5 \pm 5.7$. Here, we compute previously-neglected foreground biases in temperature-based $f_{\rm NL}^{\rm loc}$ measurements. We consider the integrated Sachs-Wolfe (ISW) effect, gravitational lensing, the thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects, and the cosmic infrared background (CIB). In standard analyses, a significant foreground bias arising from the ISW-lensing bispectrum is subtracted from the $f_{\rm NL}^{\rm loc}$ measurement. However, many other terms sourced by the ISW, lensing, tSZ, kSZ, and CIB fields are also present in the temperature bispectrum. We compute the dominant biases on $f_{\rm NL}^{\rm loc}$ arising from these signals. Most of the biases are non-blackbody, and are thus reduced by multifrequency component separation methods; however, recent analyses have found that extragalactic foregrounds are present at non-negligible levels in the Planck component-separated maps. Moreover, the Planck FFP8 simulations do not include the correlations amongst components that are responsible for these biases. We compute the biases for individual frequencies, finding that some are comparable to the statistical error bar on $f_{\rm NL}^{\rm loc}$, even for the main CMB channels (100, 143, and 217 GHz). For future experiments, they can greatly exceed the statistical error bar (considering temperature only). A full assessment will require calculations in tandem with component separation, ideally using simulations. Similar biases will also afflict measurements of equilateral and orthogonal NG, as well as trispectrum NG. We conclude that the search for primordial NG using Planck data may not yet be over.

[262] arXiv:1807.07294v1 [pdf, vox]

The variability of the warm absorber in I Zwicky 1 as seen by XMM-Newton

C. V. Silva, E. Costantini, M. Giustini, G. A. Kriss, W. N. Brandt, L. C. Gallo, D. R. Wilkins
Submitted Thursday 19 July 2018 @ 08:52:04 GMT
10 pages, 7 figures. Accepted for publication in MNRAS

We present new XMM-Newton observations of the intriguing warm absorber in I Zwicky 1. This luminous and nearby narrow-line Seyfert 1 galaxy shows ionized absorption by two components of outflowing gas; a low and a high-ionization phase with log $\xi$~0 and log $\xi$~2 respectively. Detailed modelling of these data reveal a complex and variable multi-phase warm absorber. However, we find the changes in the ionization state of the gas not to be straightforwardly correlated with the variability of the intrinsic continuum source, in apparent contrast with photoionization equilibrium. The observed variability hints instead at a close connection between the two gas components, possibly both directly connected to the accretion disc activity. We thus suggest a phenomenological model capable of explaining these observations, consisting of a clumpy outflow where the high and the low-ionization components are closely linked. Changes in ionization over the years are mainly driven by the different densities of the clumps crossing the observer's line-of-sight, in which the `skin' layer facing the source accounts for the more ionized component.

[263] arXiv:1807.07287v1 [pdf, vox]

Probing modified gravity in cosmic filaments

Alex Ho, Max Gronke, Bridget Falck, David F. Mota
Submitted Thursday 19 July 2018 @ 08:31:34 GMT
11 pages, 17 figures, submitted to A&A

Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models -- `screened' modified gravity theories -- on cosmic filaments. We utilize the $N$-body code ISIS/RAMSES to simulate the symmetron model and the Hu-Sawicky $f(R)$ model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web. We investigate how the global properties of the filaments -- such as their lengths, masses, and thicknesses -- as well as their radial density and speed profiles change under different gravity theories. We find that filaments are, on average, shorter and denser in modified gravity models compared to in $\Lambda$CDM. We also find that the speed profiles of the filaments are enhanced, consistent with theoretical expectations. Overall, our results suggest that cosmic filaments can be an effective complementary probe of screened modified gravity theories on Mpc scales.

[264] arXiv:1807.07565v1 [pdf, vox]

Detection of 25 new rotating radio transients at 111 MHz

Sergey A. Tyul'bashev, Vladislav S. Tyul'bashev, Valery M. Malofeev
Submitted Thursday 19 July 2018 @ 08:24:26 GMT
6 pages, 3 figures, 1 table; Astronomy and Astrophysics in press

Nearly all fast radio RRAT-type transients that are pulsars with rare pulses have been previously detected using decimetre wavelengths. We present here 34 transients detected at metre wavelengths in our daily monitoring at declinations -9o < decl. < +42o. 25 transients are new RRATs. We confirmed the detection of 7 RRATs based on our early observations. One of the 34 detected transients was determined to be a new pulsar J1326+3346. At the same time, out of 35 RRATs detected at the decimetre wavelengths and included in the studied area, only one was detected by us J1848+1518. The periods of 6 RRATs were found from the time of arrival of single pulses. Three quarters of all RRATs were observed more than once and the total number of RRATs in the area studied has doubled.

[265] arXiv:1807.07274v1 [pdf, vox]

Finding closure: approximating Vlasov-Poisson using finitely generated cumulants

Cora Uhlemann
Submitted Thursday 19 July 2018 @ 07:50:53 GMT
17 pages, 1 figure

Since dark matter almost exclusively interacts gravitationally, the phase-space dynamics is described by the Vlasov-Poisson equation. A key characteristic is its infinite cumulant hierarchy, a tower of coupled evolution equations for the cumulants of the phase-space distribution. While on large scales the matter distribution is well described as a fluid and the hierarchy can be truncated, smaller scales are in the multi-stream regime in which all higher-order cumulants are sourced through nonlinear gravitational collapse. This regime is crucial for the formation of bound structures and the emergence of characteristic properties such as their density profiles. We present a novel closure strategy for the cumulant hierarchy that is inspired by finitely generated cumulants and hence beyond truncation. This constitutes a constructive approach for reducing nonlinear phase-space dynamics of Vlasov-Poisson to a closed system of equations in position space. Using this idea, we derive Schr\"odinger-Poisso​n as approximate quantal method for solving classical dynamics of Vlasov-Poisson with cold initial conditions. Our deduction complements the common reverse inference of the Schr\"odinger-Vlasov relation using a semi-classical limit of quantum dynamics and provides a clearer picture of the correspondence between classical and quantal dynamics. Our framework outlines an essential first step towards constructing approximate methods for Vlasov-like systems in cosmology and plasma physics with different initial conditions and potentials.

[266] arXiv:1807.07272v1 [pdf, vox]

High-resolution observations of the symbiotic system R Aqr. Direct imaging of the gravitational effects of the secondary on the stellar wind

V. Bujarrabal, J. Alcolea, J. Mikolajewska, A. Castro-Carrizo, S. Ramstedt
Submitted Thursday 19 July 2018 @ 07:47:42 GMT
Accepted by Astronomy & Astrophysics. 7 pages, 6 figures

We have observed the symbiotic stellar system R Aqr, aiming to describe the gravitational interaction between the white dwarf (WD) and the wind from the Mira star, the key phenomenon driving the symbiotic activity and the formation of nebulae in such systems. We present high-resolution ALMA maps of the 12CO and 13CO J=3-2 lines, the 0.9 mm continuum distribution, and some high-excitation molecular lines in R Aqr. The maps, which have resolutions ranging between 40 milliarcsecond (mas) and less than 20 mas, probe the circumstellar regions at suborbital scales as the distance between the stars is ~ 40 mas. Our observations show the gravitational effects of the secondary on the stellar wind. The AGB star was identified in our maps from the continuum and molecular line data, and we estimated the probable position of the secondary from a new estimation of the orbital parameters. The (preliminary) comparison of our maps with theoretical predictions is surprisingly satisfactory and the main expected gravitational effects are directly mapped for the first time. We find a strong focusing in the equatorial plane of the resulting wind, which shows two plumes in opposite directions that have different velocities and very probably correspond to the expected double spiral due to the interaction. Our continuum maps show the very inner regions of the nascent bipolar jets, at scales of some AU. Continuum maps obtained with the highest resolution show the presence of a clump that very probably corresponds to the emission of the ionized surroundings of the WD and of a bridge of material joining both stars, which is likely material flowing from the AGB primary to the accretion disk around the WD secondary.

[267] arXiv:1807.07269v1 [pdf, vox]

The metal-rich halo component extended in z: a characterization with Gaia DR2 and APOGEE

Emma Fernández-Alvar, J. G. Fernández-Trincado, Edmundo Moreno, William J. Schuster, Leticia Carigi, Alejandra Recio-Blanco, Timothy C. Beers, Cristina Chiappini, Friedrich Anders, Basílio X. Santiago, Anna B. A. Queiroz, Ángeles Pérez-Villegas, Olga Zamora, D. A. García-Hernández
Submitted Thursday 19 July 2018 @ 07:38:32 GMT
16 pages, 12 figures, paper submitted to MNRAS

We report an analysis of the metal-rich tail ([Fe/H] $> -0.75$) of halo stars located at distances from the Galactic plane $z$ up to $|z| \sim 10$ kpc, observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We examine the chemistry, kinematics, and dynamics of this metal-rich halo sample using chemical abundances and radial velocities provided by the fourteenth APOGEE data release (DR14) and proper motions from the second Gaia data release (DR2). The analysis reveals three chemically different stellar populations in the [Mg/Fe] vs. [Fe/H] space -- the two distinct halo populations already reported in the literature, and a third group with intermediate [Mg/Fe] $\sim$+0.1. We derive the $U$, $V$ and $W$ velocity components with respect to the Local Standard of Rest, as well as orbits for the three stellar groups, and find that they differ also in their kinematical and dynamical properties. The high-[Mg/Fe] population exhibits a mean prograde rotation, as well as orbits that are more bound and closer to the plane, whereas the low-[Mg/Fe] population has $<V>$ closer to 0, and stars that move in less-bound orbits reaching larger distances from the centre and the Galactic plane. The intermediate-Mg stars exhibit different orbital characteristics, moving with a strong prograde rotation and low excentricity, but in less-bound orbits. This stellar population resembles the two stellar overdensities lying about $|z| \sim 5$ kpc recently reported in the literature, for which a disc origin has been claimed.

[268] arXiv:1807.06594v2 [pdf, vox]

A 100-pc Scale, Fast and Dense Outflow in Narrow-Line Seyfert 1 Galaxy IRAS04576+0912

Toshihiro Kawaguchi, Shinobu Ozaki, Hajime Sugai, Kazuya Matsubayashi, Takashi Hattori, Atsushi Shimono, Kentaro Aoki, Yutaka Hayano, Yosuke Minowa, Kazuma Mitsuda, Yasuhito Hashiba
Submitted Thursday 19 July 2018 @ 07:35:28 GMT
7 pages, 2 figures, Accepted for publication in PASJ

We report the initial result of an adaptive-optics assisted, optical integral-field-unit observation on IRAS04576+0912, the nearest (z=0.039) active galactic nucleus with a prominent blueshift/tail in [O III] emission from a sample of such objects that we have collected from the literature. We aim at addressing the putative quasar-mode feedback process with Subaru/Kyoto 3D II+AO188. The optical waveband (6400--7500 AA) enables us to measure the gas density via the [S II] doublets, in contrast to earlier Near-IR studies. Since the fast [O III] outflow happens only around rapidly growing central black holes, this object is suitable for investigating the black hole-galaxy coevolution. The obtained data cube exhibits blue tail in the [S II] emission at many lenslets. By fitting the spectrum with the high excess flux at the [S II] blue tail, we find the fast (~ 860 km/s), dense (>3000/cc), wide-angle and offset outflow in central 100-pc scales. Although the large opening angle and the high gas outflow-to-accretion ratio may favour the feedback hypothesis, the inferred kinetic power injection rate of this ionized gas outflow seems insufficient to influence the whole host galaxy. A conventional assumption of a low density must have overestimated the feedback process.

[269] arXiv:1807.07252v1 [pdf, vox]

Exploring the Nature of the 2016 γ-ray Emission in the Blazar 1749+096

Dae-Won Kim, Sascha Trippe, Sang-Sung Lee, Jae-Young Kim, Juan-Carlos Algaba, Jeffrey Hodgson, Jongho Park, Motoki Kino, Guang-Yao Zhao, Kiyoaki Wajima, Jee Won Lee, Sincheol Kang
Submitted Thursday 19 July 2018 @ 06:24:45 GMT
11 pages, 7 figures, 2 tables. To appear in MNRAS (submitted: 2018 May 9; accepted: 2018 July 15)

Recent Fermi-Large Area Telescope (LAT) light curves indicate an active $\gamma$-ray state spanning about five months from 2016 June to 2016 October in the BL Lac object 1749+096 (OT 081). During this period, we find two notable $\gamma$-ray events: an exceptionally strong outburst followed by a significant enhancement (local peak). In this study, we analyze multi-waveband light curves (radio, optical, X-ray, and $\gamma$-ray) plus very-long baseline interferometry (VLBI) data to investigate the nature of the $\gamma$-ray events. The $\gamma$-ray outburst coincides with flux maxima at longer wavelengths. We find a spectral hardening of the $\gamma$-ray photon index during the $\gamma$-ray outburst. The photon index shows a transition from a softer-when-brighter to a harder-when-brighter trend at around 1.8 $\times$ $10^{-7}$ ph cm$^{-2}$ s$^{-1}$. We see indication that both the $\gamma$-ray outburst and the subsequent enhancement precede the propagation of a polarized knot in a region near the VLBI core. The highest polarized intensity, 230\,mJy, and an electric vector position angle rotation, by $\sim$32$^{\circ}$, are detected about 12 days after the $\gamma$-ray outburst. We conclude that both $\gamma$-ray events are caused by the propagation of a disturbance in the mm-wave core.

[270] arXiv:1807.07251v1 [pdf, vox]

ASASSN-14dq: A fast-declining type II-P Supernova in a low-luminosity host galaxy

Avinash Singh, S. Srivastav, Brajesh Kumar, G. C. Anupama, D. K. Sahu
Submitted Thursday 19 July 2018 @ 06:19:27 GMT
28 pages, 29 figures, Accepted in MNRAS

Optical broadband (UBVRI) photometric and low-resolution spectroscopic observations of the type II-P supernova (SN) ASASSN-14dq are presented. ASASSN-14dq exploded in a low-luminosity/metal​licity host galaxy UGC 11860, the signatures of which are present as weak iron lines in the photospheric phase spectra. The SN has a plateau duration of $\sim\,$90 d, with a plateau decline rate of 1.38 $\rm mag\ (100 d)^{-1}$ in V-band which is higher than most type II-P SNe. ASASSN-14dq is a luminous type II-P SN with a peak $V$-band absolute magnitude of -17.7$\,\pm\,$0.2 mag. The light curve of ASASSN-14dq indicates it to be a fast-declining type II-P SN, making it a transitional event between the type II-P and II-L SNe. The empirical relation between the steepness parameter and $\rm ^{56}Ni$ mass for type II SNe was rebuilt with the help of well-sampled light curves from the literature. A $\rm ^{56}Ni$ mass of $\sim\,$0.029 M$_{\odot}$ was estimated for ASASSN-14dq, which is slightly lower than the expected $\rm ^{56}Ni$ mass for a luminous type II-P SN. Using analytical light curve modelling, a progenitor radius of $\rm \sim3.6\times10^{13}​$ cm, an ejecta mass of $\rm \sim10\ M_{\odot}$ and a total energy of $\rm \sim\,1.8\times 10^{51}$ ergs was estimated for this event. The photospheric velocity evolution of ASASSN-14dq resembles a type II-P SN, but the Balmer features (H$\alpha$ and H$\beta$) show relatively slow velocity evolution. The high-velocity H$\alpha$ feature in the plateau phase, the asymmetric H$\alpha$ emission line profile in the nebular phase and the inferred outburst parameters indicate an interaction of the SN ejecta with the circumstellar material (CSM).

[271] arXiv:1807.07245v1 [pdf, vox]

Young radio jets breaking free: molecular and HI outflows in their centers

Raffaella Morganti, Tom Oosterloo, Robert Schulz, Clive Tadhunter, J. B. Raymond Oonk
Submitted Thursday 19 July 2018 @ 05:41:11 GMT
Proceedings of IAU-S342 -- Perseus in Sicily: from black hole to cluster outskirts -- K. Asada, E. de Gouveia dal Pino, H. Nagai, R. Nemmen, M. Giroletti, eds - 6 pages, 3 figures

Our view of the central regions of AGN has been enriched by the discovery of fast and massive outflows of HI and molecular gas. Here we present a brief summary of results obtained for young (and restarted) radio AGN. We find that HI outflows tend to be particularly common in this group of objects. This supports the idea that the jet, expanding in a clumpy medium, plays a major role in driving these outflows. The clumpiness of the medium is confirmed by VLBI and ALMA observations. The HI observations reveal that, at least part of the gas, is distributed in clouds with sizes up to a few tens of pc and mass ~10^4 Msun. A change of the conditions in the outflow, with an increasing fraction of diffuse components, as the radio jets grow, is suggested by the high resolution HI observations. The molecular gas completes the picture, showing that the radio plasma jet can couple well with the ISM, strongly affecting the kinematics, but also the physical conditions of the molecular gas. This is confirmed by numerical simulations reproducing, to first order, the kinematics of the gas.

[272] arXiv:1807.07234v1 [pdf, vox]

Probing gravitational wave polarizations with Advanced LIGO, Advanced Virgo and KAGRA

Yuki Hagihara, Naoya Era, Daisuke Iikawa, Hideki Asada
Submitted Thursday 19 July 2018 @ 04:11:43 GMT
14 pages, 4 figures

Assuming that, for a given source of gravitational waves (GWs), we know its sky position, as a case of GW events with an electromagnetic counterpart such as GW170817, we discuss a null stream method to probe GW polarizations including spin-0 (scalar) GW modes and spin-1 (vector) modes, especially with an expected network of Advanced LIGO, Advanced Virgo and KAGRA. For two independent null streams for four unaligned GW detectors, we study a location on the sky, exactly at which the spin-0 modes of GWs vanish in any null stream for the GW detector network, though the strain output at a detector may contain the spin-0 modes. Our numerical calculations show that there exist seventy-two sky positions that satisfy this condition of killing the spin-0 modes in the null streams. If a GW source with an electromagnetic counterpart is found in one of the seventy-two sky positions, the spin-1 modes will be testable separately from the spin-0 modes by the null stream method. In addition, we study a superposition of the two null streams to show that any one of the three modes (one combined spin-0 and two spin-1 modes) can be eliminated by suitably adjusting a weighted superposition of the null streams and thereby a set of the remaining polarization modes can be experimentally tested.

[273] arXiv:1807.07221v1 [pdf, vox]

Direct detection of mirror helium dark matter in the CRESST-III experiment

R. Foot
Submitted Thursday 19 July 2018 @ 02:34:16 GMT
5 pages

Within the context of mirror dark matter, the dominant mass component of the Milky Way dark halo consists of mirror helium ions. Mirror helium can interact with ordinary matter if the kinetic mixing interaction exists. Mirror helium being rather light, $m \simeq 3.73$ GeV, generally produces sub-keV recoils in direct detection experiments. Recently, the CRESST-III experiment has began probing the sub-keV recoil energy region and is currently the most sensitive probe of such particles. We point out here that the small excess seen in the low energy recoil data obtained in the CRESST-III experiment is consistent with mirror helium scattering if the kinetic mixing parameter is around $\epsilon \approx 5 \times 10^{-10}$. This kinetic mixing strength lies within the estimated range favoured by small scale structure considerations.

[274] arXiv:1807.06761v2 [pdf, vox]

Characterization of microdot apodizers for imaging exoplanets with next-generation space telescopes

Manxuan Zhang, Garreth Ruane, Jacques-Robert Delorme, Dimitri Mawet, Nemanja Jovanavic, Jeffrey Jewell, Stuart Shaklan, J. Kent Wallace
Submitted Thursday 19 July 2018 @ 02:27:37 GMT
Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave

A major science goal of future, large-aperture, optical space telescopes is to directly image and spectroscopically analyze reflected light from potentially habitable exoplanets. To accomplish this, the optical system must suppress diffracted light from the star to reveal point sources approximately ten orders of magnitude fainter than the host star at small angular separation. Coronagraphs with microdot apodizers achieve the theoretical performance needed to image Earth-like planets with a range of possible telescope designs, including those with obscured and segmented pupils. A test microdot apodizer with various bulk patterns (step functions, gradients, and sinusoids) and 4 different dot sizes (3, 5, 7, and 10 $\mu$m) made of small chrome squares on anti-reflective glass was characterized with microscopy, optical laser interferometry, as well as transmission and reflectance measurements at wavelengths of 600 and 800 nm. Microscopy revealed the microdots were fabricated to high precision. Results from laser interferometry showed that the phase shifts observed in reflection vary with the local microdot fill factor. Transmission measurements showed that microdot fill factor and transmission were linearly related for dot sizes >5 $\mu$m. However, anomalously high transmittance was measured when the dot size is <5x the wavelength and the fill factor is approximately 50%, where the microdot pattern becomes periodic. The transmission excess is not as prominent in the case of larger dot sizes suggesting that it is likely to be caused by the interaction between the incident field and electronic resonances in the surface of the metallic microdots. We used our empirical models of the microdot apodizers to optimize a second generation of reflective apodizer designs and confirmed that the amplitude and phase of the reflected beam closely matches the ideal wavefront.

[275] arXiv:1807.07211v1 [pdf, vox]

Subband Image Reconstruction using Differential Chromatic Refraction

Matthias Lee, Tamas Budavari, Ian Sullivan, Andrew Connolly
Submitted Thursday 19 July 2018 @ 01:34:58 GMT

Refraction by the atmosphere causes the positions of sources to depend on the airmass through which an observation was taken. This shift is dependent on the underlying spectral energy of the source and the filter or bandpass through which it is observed. Wavelength-dependent refraction within a single passband is often referred to as differential chromatic refraction (DCR). With a new generation of astronomical surveys undertaking repeated observations of the same part of the sky over a range of different airmasses and parallactic angles, DCR should be a detectable and measurable astrometric signal. In this paper we introduce a novel procedure that takes this astrometric signal and uses it to infer the underlying spectral energy distribution of a source; we solve for multiple latent images at specific wavelengths via a generalized deconvolution procedure built on robust statistics. We demonstrate the utility of such an approach for estimating a partially deconvolved image, at higher spectral resolution than the input images, for surveys such as the Large Synoptic Survey Telescope (LSST).

[276] arXiv:1807.07202v1 [pdf, vox]

Gauge-ready formulation of cosmological perturbations in scalar-vector-tensor theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa
Submitted Thursday 19 July 2018 @ 00:47:37 GMT
27 pages

In scalar-vector-tensor (SVT) theories with parity invariance, we perform a gauge-ready formulation of cosmological perturbations on the flat Friedmann-Lema\^{i}t​re-Robertson-Walker (FLRW) background by taking into account a matter perfect fluid. We derive the second-order action of scalar perturbations and resulting linear perturbation equations of motion without fixing any gauge conditions. Depending on physical problems at hand, most convenient gauges can be chosen to study the development of inhomogeneities in the presence of scalar and vector fields coupled to gravity. This versatile framework, which encompasses Horndeski and generalized Proca theories as special cases, is applicable to a wide variety of cosmological phenomena including nonsingular cosmology, inflation, and dark energy. By deriving conditions for the absence of ghost and Laplacian instabilities in several different gauges, we show that, unlike Horndeski theories, it is possible to evade no-go arguments for the absence of stable nonsingular bouncing/genesis solutions in both generalized Proca and SVT theories. We also apply our framework to the case in which scalar and vector fields are responsible for dark energy and find that the separation of observables relevant to the evolution of matter perturbations into tensor, vector, and scalar sectors is transparent in the unitary gauge. Unlike the flat gauge chosen in the literature, this result is convenient to confront SVT theories with observations associated with the cosmic growth history.

[277] arXiv:1807.07195v1 [pdf, vox]

A catalog of merging dwarf galaxies in the local universe

Sanjaya Paudel, Rory Smith, Suk Jin Yoo, Paula Calderón-Castillo, Pierre-Alain Duc
Submitted Thursday 19 July 2018 @ 00:32:47 GMT
26 Pages, Accepted for publication in ApJS

We present the largest publicly available catalog of interacting dwarf galaxies. It includes 177 nearby merging dwarf galaxies of stellar mass M$_{*}$ $<$ 10$^{10}$M$_{\sun}$ and redshifts z $<$ 0.02. These galaxies are selected by visual inspection of publicly available archival imaging from two wide-field optical surveys (SDSS III and the Legacy Survey), and they possess low surface brightness features that are likely the result of an interaction between dwarf galaxies. We list UV and optical photometric data which we use to estimate stellar masses and star formation rates. So far, the study of interacting dwarf galaxies has largely been done on an individual basis, and lacks a sufficiently large catalog to give statistics on the properties of interacting dwarf galaxies, and their role in the evolution of low mass galaxies. We expect that this public catalog can be used as a reference sample to investigate the effects of the tidal interaction on the evolution of star-formation, morphology/structure of dwarf galaxies. Our sample is overwhelmingly dominated by star-forming galaxies, and they are generally found significantly below the red-sequence in the color-magnitude relation. The number of early-type galaxies is only 3 out of 177. We classify them, according to observed low surface brightness features, into various categories including shells, stellar streams, loops, antennae or simply interacting. We find that dwarf-dwarf interactions tend to prefer the low density environment. Only 41 out of the 177 candidate dwarf-dwarf interaction systems have giant neighbors within a sky projected distance of 700 kpc and a line of sight radial velocity range $\pm$700 km/s and, compared to the LMC-SMC, they are generally located at much larger sky-projected distances from their nearest giant neighbor.

[278] arXiv:1807.06664v2 [pdf, vox]

SOFIA/HAWC+ detection of a gravitationally lensed starburst galaxy at $z$ = 1.03

Jingzhe Ma, Arianna Brown, Asantha Cooray, Hooshang Nayyeri, Hugo Messias, Nicholas Timmons, Johannes Staguhn, Pasquale Temi, C. Darren Dowell, Julie Wardlow, Dario Fadda, Attila Kovacs, Dominik Riechers, Ivan Oteo, Derek Wilson, Ismael Perez-Fournon
Submitted Thursday 19 July 2018 @ 00:31:38 GMT
8 pages, 3 figures; accepted for publication in ApJ

We present the detection at 89 $\mu$m (observed frame) of the {\it Herschel}-selected gravitationally lensed starburst galaxy HATLASJ1429-0028 (also known as G15v2.19) in 15 minutes with the High-resolution Airborne Wideband Camera-plus (HAWC+) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectacular lensing system consists of an edge-on foreground disk galaxy at $z$ = 0.22 and a nearly complete Einstein ring of an intrinsic ultra-luminous infrared galaxy at $z$ = 1.03. Is this high IR luminosity powered by pure star formation (SF) or also an active galactic nucleus (AGN)? Previous nebular line diagnostics indicate that it is star-formation dominated. We perform a 27-band multi-wavelength spectral energy distribution modeling (SED) including the new SOFIA/HAWC+ data to constrain the fractional AGN contribution to the total IR luminosity. The AGN fraction in the IR turns out to be negligible. In addition, J1429-0028 serves as a testbed for comparing SED results from different models/templates and SED codes (MAGPHYS, SED3FIT, and CIGALE). We stress that star formation history is the dominant source of uncertainty in the derived stellar mass (as high as a factor of $\sim$ 10) even in the case of extensive photometric coverage. Furthermore, the detection of a source at $z$ $\sim$ 1 with SOFIA/HAWC+ demonstrates the potential of utilizing this facility for distant galaxy studies including the decomposition of SF/AGN components, which cannot be accomplished with other current facilities.

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