H Galaxy Survey (HGS)

We are undertaking a major survey of star formation in the local Universe, using the Jacobus Kapteyn Telescope and redshifted H filters to determine the quantity and spatial distribution of ionized gas in ~450 spiral and irregular galaxies within 30 h^-1Mpc. The resulting dataset should yield new insights into such fundamental questions as the total star formation rate at the current epoch, the types of galaxies and galaxy environments which dominate this overall rate, and how star formation regions are distributed within their host galaxies.

One of the major areas of recent interest in extragalactic astronomy has been the evolution in the total star formation rate of the Universe as a function of cosmological look-back time (e.g. Madau et al. 1996), with the apparent identification of a star formation peak at redshifts 1-2. However, there are still many gaps in our understanding of star formation in the local Universe, and for example both the total rate, and the types of galaxy which dominate total star formation, are still poorly understood. We propose to address these questions and others by a large survey of H emission from star formation regions and nuclei of spiral and irregular galaxies.

We will image 450 carefully selected spiral and irregular galaxies, with recession velocities up to 3000~km/s, in redshifted H filters. Measured H fluxes from HII regions can be converted into total star formation rates (see e.g. Kennicutt 1983), and will enable us to address the following questions:

What is the total star formation rate in the local Universe, and which galaxy types dominate?
How do environment (field, group or cluster and nearby neighbours) and galaxy morphology (B/D ratio, bar strength, disk asymmetry) affect star formation rate?
Does nuclear activity (star formation or AGN) depend on galaxy properties and environment?
Where drives the star formation distribution within galaxies? Can density wave theory explain this distribution? Where does star formation occur with respect to the bulge, bar and disk, spiral arms and rings? If interactions enhance star formation, where in the galaxy?

galaxy surveys have been carried out in the past, although not for a well-selected, volume limited sample as proposed here. Kennicutt and Kent (1983) presented H

measurements from a combination of slit spectroscopy and narrow-band imaging for ~200 field and Virgo cluster galaxies, mainly bright spirals. Young et al. (1996) observed 120 spiral galaxies, of types S0-Sdm plus some irregulars, and found a good correlation between H

luminosity and far-IR luminosity, confirming that H

is a good indicator of star formation rate. This shows that extinction, [NII] contamination and H

absorption, all of which could potentially affect measured H

flux as a measure of star formation rate, are not so large as to prevent star formation rates to be estimated using this technique.

A key feature of this survey, compared with those of Kennicutt & Kent (1983) and Young (1996), is that we propose to map a representative volume of the Universe, rather than simply sampling bright galaxies with a range of Hubble types. Ours is much the more ambitious task, and requires a large sample of galaxies. Indeed, de Jong and Lacey (1999) calculate that to sample the full range of surface brightness and Hubble type observed in galaxies requires of order 1000 galaxies. Our sample was selected using the Uppsala Galaxy Catalogue (Nilson et al. 1973) as the parent catalogue, within 5 redshift shells, of 0-1000~kms^-1, 1000-1500~kms^-1 1500-2000~kms^-1, 2000-2500~kms^-1, and 2500-3000~kms^-1, but with the angular area decreasing such that the shell volume remained constant. The galaxies were required to be spirals, with type S0/a-Im inclusive, and D₂₅ diameters 1.5-6.0 arcmin. This last criterion ensures that all galaxies will fit on the JKT CCD field, and the different shells effectively sample different parts of the galaxy diameter function. Thus the central shell is dominated by dwarf Im and Sm galaxies, whilst the outer shells sample the rarer S0/a-Sc alaxies. The well-defined selection criteria, and the large total number of galaxies (450), mean that it will be possible to combine the data for all shells such that galaxies with a wide range of luminosities, diameter and surface rightnesses are represented. Previous studies, e.g. those of Kennicutt and Kent (1983) and Young et al. (1996), have been weighted heavily towards large, luminous and relatively rare Sa-Sc spirals with a narrow range in surface brightness and scale size.
References

de Jong R.S., Lacey C., 1999, Proc. I.A.U. Colloquium 171, ``The low surface brightness Universe'' (astro-ph 9810511)
Madau P., Ferguson H.C., Dickinson M.E., Giavalisco M., Steidel C.C., Fruchter A., 1996, MNRAS, 283, 1388
Keel W.C., Kennicutt R.C., Hummel E., van der Hulst J.M., 1985, AJ, 90, 708
Kennicutt R.C., 1983, ApJ, 272, 54
Kennicutt R.C., 1984, ApJ, 287, 116
Kennicutt R.C., Kent S.M., 1983, AJ, 88, 1094
Nilson, P., 1973, ``Uppsala general catalogue of galaxies''
Young J.S., Allen L., Kenney J.D.P., Rownd B., 1996, AJ, 112, 1903

Full list of collaborators

Phil James
Chris Collins
Jason Etherton
Lee Howells
Chris Moss
Susan Percival
Neville Shane
Iain Steele
(all from Liverpool John Moores University)

John Beckman, Instituto de Astrofisica de Canarias.
Roelof de Jong, Steward Observatory, Univ. Arizona.
Johan Knapen, Univ. Hertfordshire & ING
Sharon Stedman, Univ. Hertfordshire.
Reynier Peletier, Univ. Nottingham.
Don Pollacco, Univ. Belfast.
Marc Seigar, Imperial College.

Data:

These lists are sorted in order of redshift bin (recession velocity):

0-1000 kms^-1 | 1000-1500 kms^-1 | 1500-2000 kms^-1 | 2000-2500 kms^-1 | 2500-3000 kms^-1

User notes:

Notes for observers | Observing log | Filter notes | Flux standards

Papers:

Published papers | Papers in preparation | Reduced FITS

The "Papers in Preparation" link requires the HaGS password.

je@astro.livjm.ac.uk