The Assembly of the Red Sequence at z~1: The Color and Spectral
  Properties of Galaxies in the Cl1604 Supercluster
  We investigate the properties of the 525 spectroscopically confirmed members
of the Cl1604 supercluster at z~0.9 as part of the Observations of Redshift
Evolution in Large Scale Environments (ORELSE) survey. Using extensive Keck
LRIS/DEIMOS spectroscopy in conjunction with ten-band ground-based, Spitzer,
and HST imaging, we investigate the buildup of the red sequence in groups and
clusters at high redshift. Nearly all of the brightest and most massive
red-sequence galaxies are found within the bounds of the clusters and groups.
Despite the prevalence of these red-sequence galaxies, we find that the average
cluster galaxy has a spectrum indicative of a star-forming galaxy, with a star
formation rate between those of z~1 field galaxies and moderate redshift
cluster galaxies. The average group galaxy is even more active, exhibiting
properties indicative of a starburst. The presence of massive, red galaxies and
the high fraction of starbursting galaxies suggest that significant processing
is occurring in the group environment at z~1 and earlier. There is a deficit of
low-luminosity red-sequence galaxies in all Cl1604 clusters and groups,
suggesting that such galaxies transition to the red sequence at later times.
Extremely massive (10^12) red sequence galaxies are also absent from the Cl1604
clusters and groups. We suggest that such galaxies form at later times through
merging processes. There are also large populations of transition galaxies at
intermediate stellar masses present in the groups and clusters, suggesting that
such masses are important in the buildup of the red-sequence mass function at
z~1. Through a comparison of the transitional populations present in the Cl1604
clusters and groups, we find evidence that massive blue cloud galaxies are
quenched earliest in the most dynamically relaxed systems and at progressively
later times in dynamically unrelaxed systems.
