Galaxies in X-ray Selected Clusters and Groups in Dark Energy Survey
  Data I: Stellar Mass Growth of Bright Central Galaxies Since z~1.2
  Using the science verification data of the Dark Energy Survey (DES) for a new
sample of 106 X-Ray selected clusters and groups, we study the stellar mass
growth of Bright Central Galaxies (BCGs) since redshift 1.2. Compared with the
expectation in a semi-analytical model applied to the Millennium Simulation,
the observed BCGs become under-massive/under-luminous with decreasing redshift.
We incorporate the uncertainties associated with cluster mass, redshift, and
BCG stellar mass measurements into analysis of a redshift-dependent BCG-cluster
mass relation, $m_{*}\propto(\frac{M_{200}}{1.5\times
10^{14}M_{\odot}})^{0.24\pm 0.08}(1+z)^{-0.19\pm0.34}$, and compare the
observed relation to the model prediction. We estimate the average growth rate
since $z = 1.0$ for BCGs hosted by clusters of $M_{200, z}=10^{13.8}M_{\odot}$,
at $z=1.0$: $m_{*, BCG}$ appears to have grown by $0.13\pm0.11$ dex, in tension
at $\sim 2.5 \sigma$ significance level with the $0.40$ dex growth rate
expected from the semi-analytic model. We show that the buildup of extended
intra-cluster light after $z=1.0$ may alleviate this tension in BCG growth
rates.
