Central and Satellite Colors in Galaxy Groups: A Comparison of the Halo   Model and SDSS Group Catalogs
  Current analytic and semi-analytic dark matter halo models distinguish between the central galaxy in a halo and the satellite galaxies in halo substructures. Using a recent halo-model description of the color dependence of galaxy clustering (Skibba & Sheth 2008), we investigate the colors of central and satellite galaxies predicted by the model and compare them to those of two galaxy group catalogs constructed from the Sloan Digital Sky Survey (Yang et al. 2007, Berlind et al. 2006a). In the model, the environmental dependence of galaxy color is determined by that of halo mass, and the predicted color mark correlations were shown to be consistent with SDSS measurements. The model assumes that satellites tend to follow a color-magnitude sequence that approaches the red sequence at bright luminosities; the model's success suggests that bright satellites tend to be `red and dead' while the star formation in fainter ones is in the process of being quenched. In both the model and the SDSS group catalogs, we find that at fixed luminosity or stellar mass, central galaxies tend to be bluer than satellites. In contrast, at fixed group richness or halo mass, central galaxies tend to be redder than satellites, and galaxy colors become redder with increasing mass. We also compare the central and satellite galaxy color distributions, as a function of luminosity and as a function of richness, in the model and in the two group catalogs. Except for faint galaxies and small groups, the model and both group catalogs are in very good agreement. 
Ramin A. Skibba