The Dawn of the Red: Star formation histories of group galaxies over the
  past 5 billion years
  We examine the star formation properties of group and field galaxies in two
surveys, the Sloan Digital Sky Survey (SDSS; at z ~ 0.08) and the Group
Environment and Evolution Collaboration (GEEC; at z ~ 0.4). Using UV imaging
from the GALEX space telescope, along with optical and, for GEEC, near infrared
photometry, we compare the observed spectral energy distributions to large
suites of stellar population synthesis models. This allows us to accurately
determine star formation rates and stellar masses. We find that star forming
galaxies of all environments undergo a systematic lowering of their star
formation rate between z=0.4 and z=0.08 regardless of mass. Nonetheless, the
fraction of passive galaxies is higher in groups than the field at both
redshifts. Moreover, the difference between the group and field grows with time
and is mass-dependent, in the sense the the difference is larger at low masses.
However, the star formation properties of star forming galaxies, as measured by
their average specific star formation rates, are consistent within the errors
in the group and field environment at fixed redshift. The evolution of passive
fraction in groups between z=0.4 and z=0 is consistent with a simple accretion
model, in which galaxies are environmentally affected 3 Gyrs after falling into
a ~ 10E13 Msun group. This long timescale appears to be inconsistent with the
need to transform galaxies quickly enough to ensure that star forming galaxies
appear similar in both the group and field, as observed.
