The zCOSMOS Redshift Survey: How group environment alters global
  downsizing trends
  We took advantage of the wealth of information provided by the first ~10000
galaxies of the zCOSMOS-bright survey and its group catalogue to study the
complex interplay between group environment and galaxy properties. The
classical indicator F_blue (fraction of blue galaxies) proved to be a simple
but powerful diagnostic tool. We studied its variation for different luminosity
and mass selected galaxy samples. Using rest-frame B-band selected samples, the
groups galaxy population exhibits significant blueing as redshift increases,
but maintains a lower F_blue with respect both to the global and the isolated
galaxy population. However moving to mass selected samples it becomes apparent
that such differences are largely due to the biased view imposed by the B-band
luminosity selection, being driven by the population of lower mass, bright blue
galaxies for which we miss the redder, equally low mass, counterparts. By
focusing the analysis on narrow mass bins such that mass segregation becomes
negligible we find that only for the lowest mass bin explored (logMass <= 10.6)
does a significant residual difference in color remain as a function of
environment, while this difference becomes negligible toward higher masses. Our
results indicate that red galaxies of logMass >= 10.8 are already in place at z
~ 1 and do not exhibit any strong environmental dependence, possibly
originating from so-called 'nature'/internal mechanisms. In contrast, for lower
galaxy masses and redshifts lower than z ~ 1, we observe the emergence in
groups of a population of 'nurture' red galaxies: slightly deviating from the
trend of the downsizing scenario followed by the global galaxy population, and
more so with cosmic time. These galaxies exhibit signatures of group-related
secular physical mechanisms directly influencing galaxy evolution.
