The Role of Galaxy Stellar Mass in the Colour-Density Relation up to z ~1

It is well known that galaxy properties correlate with the local environment in which galaxies reside. In contrast, it is still matter of debate why and when these environmental dependences originate, and whether only one "main" property depends on environment, thus driving all the others environmental dependences via the correlations among properties themselves. We use the first \u2dc 10, 000 spectra of the zCOSMOS sample (I = 1. 15 is higher for lower delta. Given the triple dependence among galaxy colours, stellar mass and delta, the colour-delta relation that we find can be due to the broad range of stellar masses embedded in the sample. We find that once mass is fixed the colour-delta relation is globally flat up to z \u2dc 1 for galaxies with log(M / M sun ) >= 10. 7. On the contrary, even at fixed mass we observe that within 0. 1 <= z <= 0. 5 the fraction of red galaxies with log(M / M sun ) <= 10. 7 depends on delta. We suggest a scenario in which the colour depends primarily on stellar mass, but for an intermediate mass regime (10. 2 <= log(M / M sun ) <= 10. 7) the local density modulates this dependence. These lower mass galaxies formed more recently, in an epoch when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time