Galaxies in X-ray Groups. III. Satellite Color and Morphology
  Transformations
  While the star formation rates and morphologies of galaxies have long been
known to correlate with their local environment, the process by which these
correlations are generated is not well understood. Galaxy groups are thought to
play an important role in shaping the physical properties of galaxies before
entering massive clusters at low redshift, and transformations of satellite
galaxies likely dominate the buildup of local environmental correlations. To
illuminate the physical processes that shape galaxy evolution in dense
environments, we study a sample of 116 X-ray selected galaxy groups at z=0.2-1
with halo masses of 10^13-10^14 M_sun and centroids determined with weak
lensing. We analyze morphologies based on HST imaging and colors determined
from 31 photometric bands for a stellar mass-limited population of 923
satellite galaxies and a comparison sample of 16644 field galaxies. Controlling
for variations in stellar mass across environments, we find significant trends
in the colors and morphologies of satellite galaxies with group-centric
distance and across cosmic time. Specifically at low stellar mass
(log(M_stellar/M_sun) = 9.8-10.3), the fraction of disk-dominated star-forming
galaxies declines from >50% among field galaxies to <20% among satellites near
the centers of groups. This decline is accompanied by a rise in quenched
galaxies with intermediate bulge+disk morphologies, and only a weak increase in
red bulge-dominated systems. These results show that both color and morphology
are influenced by a galaxy's location within a group halo. We suggest that
strangulation and disk fading alone are insufficient to explain the observed
morphological dependence on environment, and that galaxy mergers or close tidal
encounters must play a role in building up the population of quenched galaxies
with bulges seen in dense environments at low redshift.
