The Galaxy Color-mass-density Relation up to z=1

We use the first 10k spectra of the zCOSMOS sample (I <= 22.5) to study the role of galaxy stellar mass in the color-density relation up to z=1. We confirm (Cucciati et al 2006) that in a luminosity limited sample (M(B)=-20.5-z) red galaxies reside mainly in high densities (delta) at least up to z=1. However, it is known that stellar mass (M) depends on 6, and that color depends on M. In a luminosity (L) selected sample the spread in M/L causes a broad range in M, that biases any direct color-delta relation via the M-delta relation. Thus, we studied the color-delta relation in narrow mass bins, in three z ranges up to z=1, above some complete mass limits. We find that at fixed M the color-delta relation is generally flat, with the exception of 0.1 < z < 0.5, where the fraction of 'very red' (see the Figure) galaxies depends on delta even at fixed M, for log(M)<= 10.7. This means that the stellar mass is not the only ingredient needed to understand how environment affects galaxy colors. We suggest (Cucciati et al 2009) that galaxy color depends primarily on mass, but for relatively low masses (log(M)<= 10.7) the local density modulates this dependence: these galaxies formed more recently, when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate for longer time-scales.