Galaxy bimodality versus stellar mass and environment
Baldry et al. 2006, published in MNRAS, Vol. 373, pp. 469-483 (links:
astro-ph;
ADS).
Abstract
We analyse a z < 0.1 galaxy sample from the Sloan Digital Sky Survey
focusing on the variation of the galaxy colour bimodality with stellar
mass and projected neighbour density Sigma, and on measurements of the
galaxy stellar mass functions. The characteristic mass increases with
environmental density from about 10^10.6 Msun to 10^10.9 Msun (Kroupa
IMF, H_0=70) for Sigma in the range 0.1--10 per Mpc^2. The galaxy
population naturally divides into a red and blue sequence with the
locus of the sequences in colour-mass and colour-concentration index
not varying strongly with environment. The fraction of galaxies on the
red sequence is determined in bins of 0.2 in log Sigma and log mass
(12 x 13 bins). The red fraction f_r generally increases continuously
in both Sigma and mass such that there is a unified relation: f_r =
F(Sigma,mass). Two simple functions are proposed which provide good
fits to the data. These data are compared with analogous quantities in
semi-analytical models based on the Millennium N-body simulation: the
Bower et al. (2006) and Croton et al. (2006) models that incorporate
AGN feedback. Both models predict a strong dependence of the red
fraction on stellar mass and environment that is qualitatively similar
to the observations. However, a quantitative comparison shows that the
Bower et al. model is a significantly better match; this appears to be
due to the different treatment of feedback in central galaxies.
Data:
Galaxy stellar mass functions for 12 environment bins as per Figure 8(a).
(Stellar masses use the Kroupa '01 IMF and H_0=70. Omega_stars is about 0.002.
Note on IMF use.)
GSMF Schechter fits for 12 environment bins as per Figure 8(b-d).
GSMF double Schechter fits as per Figure A1.
Color-mass 2D histograms for 6 environment bins as per Figure 9.
Fraction of red-sequence galaxies for 13 mass x 12 environment bins as per Figures 11-12.
Spectroscopic completeness as per Figure 3.
Color-magnitude 2D histogram as per Figure 7(b).
DR7 galaxy catalog with Sigma values (6.2M),
see this file for column details.
Figures:
Environmental densities around galaxies
Bimodality in the colour-mass distribution for different environments
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