The Assembly of Galaxy Clusters
Joel C. Berrier, Kyle R. Stewart, James S. Bullock, Chris W. Purcell,, Elizabeth J. Barton (UC Irvine), Risa H. Wechsler (Stanford)

TL;DR
This study uses cosmological simulations to analyze galaxy accretion and transformation in clusters, finding most galaxies fall directly from the field and that cluster-specific processes dominate galaxy evolution.
Contribution
It provides new insights into the accretion histories and transformation timescales of cluster galaxies, emphasizing the role of local cluster processes over pre-processing.
Findings
~70% of cluster galaxies fall directly from the field.
Less than 12% are accreted as part of large groups.
Transformation timescale within clusters is approximately 6 Gyr.
Abstract
We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing in the group environment prior to their accretion into the cluster. On average, ~70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than ~12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (~6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like…
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