The Gemini/HST Galaxy Cluster Project: Environment Effects on the
  Stellar Populations in the Lynx Clusters at z=1.27
  Few detailed investigations of stellar populations in passive galaxies beyond
z~1 are based on deep spectroscopic observations, due to the difficulty in
obtaining such data. We present a study of stellar populations, structure, and
mass-to-light ratios of a large sample of bulge-dominated galaxies in the two
z=1.27 clusters Lynx E and Lynx W, based on deep ground-based optical
spectroscopy combined with imaging from Hubble Space Telescope. We find that
Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such
a core. If all the sample galaxies evolve similarly in size from z=1.27 to the
present, the data allow only 0.1 dex size-growth at a fixed dynamical mass.
However, to link the Lynx central galaxies to brightest cluster galaxies
similar to those of low redshift clusters, the Lynx galaxies would have to grow
by at least a factor five, possibly through major merging. The mass-to-light
ratios and the Balmer absorption lines of the Lynx galaxies are consistent with
passive evolution of the stellar populations from z=1.27 to the present and
support ages of 1--3 Gyr. The galaxies in the outskirts of the clusters contain
younger stellar populations than found in the cluster cores. However, when
evolved passively to z~0 both populations are consistent with the observed
populations in the Coma cluster galaxies. The bulge-dominated emission line
galaxies in the clusters are dominated by stellar populations with sub-solar
metallicities. Thus, additional enrichment of these is required to produce
Coma-like stellar populations by z~0.
