The Sloan great wall. Rich clusters (original) (raw)

2010, Astronomy & Astrophysics

THE ASSEMBLY OF GALAXY CLUSTERS

Astrophysical Journal, 2009

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 ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with ~20% incorporated into the cluster halo more than 7 Gyr ago and ~20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate timescale for late-type to early-type transformation within the cluster environment to be ~6 Gyr.

The Evolution of Galaxies in Clusters

Symposium - International Astronomical Union, 2003

We report on recent numerical investigations of the dynamical evolution of galaxies in clusters. Simulations of spiral galaxies falling into forming clusters show the development of the morphology-density relationship and the formation of regular and giant elliptical galaxies. The regular elliptical merger remnants end up in a fundamental plane very similar to the observed relation. The giant ellipticals have much in common with their real counterparts but their central velocity dispersions are too high. We also quantify the amount and distribution of diffuse light in clusters.

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