zCOSMOS 10k-bright spectroscopic sample: exploring mass and environment
  dependence in early-type galaxies
  We present the analysis of the U-V rest-frame color distribution and some
spectral features as a function of mass and environment for two sample of
early-type galaxies up to z=1 extracted from the zCOSMOS spectroscopic survey.
The first sample ("red galaxies") is defined with a photometric classification,
while the second ("ETGs") by combining morphological, photometric, and
spectroscopic properties to obtain a more reliable sample. We find that the
color distribution of red galaxies is not strongly dependent on environment for
all mass bins, with galaxies in overdense regions redder than galaxies in
underdense regions with a difference of 0.027\pm0.008 mag. The dependence on
mass is far more significant, with average colors of massive galaxies redder by
0.093\pm0.007 mag than low-mass galaxies throughout the entire redshift range.
We study the color-mass relation, finding a mean slope 0.12\pm0.005, while the
color-environment relation is flatter, with a slope always smaller than 0.04.
The spectral analysis that we perform on our ETGs sample is in good agreement
with our photometric results: we find for D4000 a dependence on mass between
high and low-mass galaxies, and a much weaker dependence on environment
(respectively a difference of of 0.11\pm0.02 and of 0.05\pm0.02); for the
equivalent width of H{\delta}we measure a difference of 0.28\pm0.08 {\AA}across
the same mass range and no significant dependence on environment.By analyzing
the lookback time of early-type galaxies, we support the possibility of a
downsizing scenario, in which massive galaxies with a stronger D4000 and an
almost constant equivalent width of $H\delta$ formed their mass at higher
redshift than lower mass ones. We also conclude that the main driver of galaxy
evolution is the galaxy mass, the environment playing a subdominant role.
