The dependence on environment of the color-magnitude relation of galaxies

The distribution in color and absolute magnitude is presented for 55,158 galaxies taken from the Sloan Digital Sky Survey in the redshift range 0.08 < z < 0.12, as a function of the galaxy number overdensity in a cylinder of transverse radius 1 h(-1) Mpc and line-of-sight half-length 8 h(-1) Mpc. In all environments, bulge-dominated galaxies ( defined to be those with radial profiles best fitted with large Sersic indices) have a color-magnitude diagram dominated by red galaxies for which the mode of the color distribution at fixed absolute magnitude depends linearly on absolute magnitude. Although the most luminous galaxies reside preferentially in high-density regions and blue galaxies reside preferentially in low-density regions, there is only a barely detectable variation with overdensity in the color ( zero point) or slope of the linear relation between the mode color and luminosity [<0.02 mag in (0.1)(g-r) or (B-V)]. These results constrain variations with environmental density in the ages or metallicities of typical bulge-dominated galaxies to be under 20%.