  The properties of galaxies are strongly correlated with their environment,
with red galaxies dominating galaxy clusters and blue galaxies dominating the
general field. However, not all field galaxies are young: studies of the
colors, line strengths, and M/L ratios of massive early-type galaxies at
0<z<1.3 show that the most massive galaxies do not seem to care about their
surroundings, and have very similar ages irrespective of their environment.
There is good evidence that the growth of these galaxies does continue longer
in the field than in clusters, via (nearly) dissipationless mergers of already
old galaxies. These results are consistent with predictions of recent galaxy
formation models, which incorporate AGN feedback to suppress star formation in
the most massive halos. Systematic studies of the relation of galaxies with
their environment beyond z=1 are difficult, and still somewhat contradictory.
Intriguingly both the DEEP2 and VVDS surveys find that the color-density
relation disappears at z~1.3, unfortunately just at the point where both
surveys become highly incomplete. On the other hand, clustering studies at
z~2.5 have shown that red galaxies cluster more strongly than blue galaxies,
implying that the color-density relation was already in place at that redshift.

Astrophysics