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∗∝(M2001.5×1014M⊙)0.24±0.08(1+z)−0.19±0.34, 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 M200,z=1013.8M⊙, at z=1.0: m∗,BCG appears to have grown by 0.13±0.11 dex, in tension at ∼2.5σ 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.