Galaxy evolution at high redshift: the legacy of deep near-infrared surveys
Exploring the progenitors of Brightest Cluster Galaxies at z~2 by CANDELS UDS
Dongyao Zhao
Christopher Conselice (University of Nottingham); Alfonso Aragon-Salamanca (University of Nottingham)
University of Nottingham
The evolution of BCGs is important for understanding galaxy assembly history within galaxy clusters, but observationally it is hard to define BCG progenitors beyond z~1. In this work, we develop a novel method for identifying BCG progenitors at z~2 and tracing the evolution of BCGs since that time. We conclude from simulations that the best method to construct BCG progenitor sample at z~2 is to use a hybrid environmental density and stellar mass ranking approach by which 44.5% of BCG progenitors can be retrieved. Applying this method on CANDELS UDS data, we construct our z~2 BCG progenitor sample. We furthermore select our local comparisons from SDSS with statistically likely contamination to ensure a fair comparison between high and low redshifts. Using these observational samples, we find that the size of BCGs has grown by a factor of 3.2 since z~2, and BCG progenitors are mainly late-type galaxies. BCG progenitors have more disturbed morphologies: 32% of them are undergoing mergers or will undergo mergers. In contrast, local BCGs are early-type galaxies having much smoother morphologies. We find that the stellar mass of BCGs has grown by a factor of 2.5 since z~2, and the SFR of BCG progenitors is much higher than their quiescent local descendants. We demonstrate that over z=1-2 SF and merging contribute equally to BCG mass growth. However, since SFR decreases with time, merging play a more dominant role in BCG assembly at redshifts lower than 1.


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