Morphology and the Color-Mass Diagram as Clues to Galaxy Evolution at
  z~1
  We study the significance of mergers in the quenching of star formation in
galaxies at z~1 by examining their color-mass distributions for different
morphology types. We perform two-dimensional light profile fits to GOODS iz
images of ~5000 galaxies and X-ray selected active galactic nucleus (AGN) hosts
in the CANDELS/GOODS-north and south fields in the redshift range 0.7<z<1.3.
Distinguishing between bulge-dominated and disk-dominated morphologies, we find
that disks and spheroids have distinct color-mass distributions, in agreement
with studies at z~0. The smooth distribution across colors for the disk
galaxies corresponds to a slow exhaustion of gas, with no fast quenching event.
Meanwhile, blue spheroids most likely come from major mergers of star-forming
disk galaxies, and the dearth of spheroids at intermediate green colors is
suggestive of rapid quenching. The distribution of moderate luminosity X-ray
AGN hosts is even across colors, in contrast, and we find similar numbers and
distributions among the two morphology types with no apparent dependence on
Eddington ratio. The high fraction of bulge-dominated galaxies that host an AGN
in the blue cloud and green valley is consistent with the scenario in which the
AGN is triggered after a major merger, and the host galaxy then quickly evolves
into the green valley. This suggests AGN feedback may play a role in the
quenching of star formation in the minority of galaxies that undergo major
mergers.
