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 galaxy number overdensity in a line-of-sight cylinder of transverse radius 1 h−1 Mpc. In all environments, bulge-dominated galaxies (defined to be those with radial profiles best fit with large Sérsic indices) form a narrow, well defined color– magnitude relation. Although the most luminous galaxies reside preferentially in the highest density regions, there is only a barely detectable variation in the color (zeropoint) or slope of the color–magnitude relation (< 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 percent. Subject headings: cosmology: observations — galaxies: clusters: general — galaxies: elliptical and lenticular, cD — galaxies: evolution — galaxies: fundamental parameters — galaxies: statistics