Tracing cosmic evolution with clusters of galaxies

Abstract

The most successful cosmological models to date envision structure formation as a hierarchical process in which gravity is constantly drawing lumps of matter together to form increasingly larger structures. Clusters of galaxies currently sit atop this hierarchy as the largest objects that have had time to collapse under the influence of their own gravity. Thus, their appearance on the cosmic scene is also relatively recent. Two features of clusters make them uniquely useful tracers of cosmic evolution. First, clusters are the biggest things whose masses we can reliably measure because they are the largest objects to have undergone gravitational relaxation and entered into virial equilibrium. Mass measurements of nearby clusters can therefore be used to determine the amount of structure in the universe on scales of 10^14 to 10^15 solar masses, and comparisons of the present-day cluster mass distribution with the mass distribution at earlier times can be used to measure the rate of structure formation, placing important constraints on cosmological models. Second, clusters are essentially ``closed boxes'' that retain all their gaseous matter, despite the enormous energy input associated with supernovae and active galactic nuclei, because the gravitational potential wells of clusters are so deep. The baryonic component of clusters therefore contains a wealth of information about the processes associated with galaxy formation, including the efficiency with which baryons are converted into stars and the effects of the resulting feedback processes on galaxy formation. This article reviews our theoretical understanding of both the dark-matter component and the baryonic component of clusters. (Abridged)Comment: 54 pages, 15 figures, Rev. Mod. Phys. (in press

Warm gas in and around simulated galaxy clusters as probed by absorption lines

“…Hot gas (T > 10 6 K) is the largest baryonic component of galaxy clusters, comprising ∼80% or more of the cluster baryon mass (Voit, 2005). For non-cool core clusters, the average ICM temperature generally decreases radially outward from cluster center (De Grandi & Molendi, 2002).…”

“…Clusters host dark matter potential wells around 10 14 -10 15 M that are able to heat the infalling gas to temperatures of 10 7 -10 8 K. This hot intracluster medium (ICM), constitutes the most significant baryonic component of galaxy clusters and is well observed in thermal X-ray emission (Voit, 2005, and references therein). The flow of gas into and out of galaxies within clusters, and into the cluster itself, is strongly affected by the cluster environment.…”

The abundance and colours of galaxies in high-redshift clusters in the cold dark matter cosmology

“…Baldry et al 2004;Bell et al 2004;Brinchmann et al 2004), with many studies supporting a high formation redshift of the stellar population of z f 2 (e.g. Ellis et al 1997;Smail et al 1998;Stanford et al 1998;Ponman, Cannon & Navarro 1999;López-Cruz, Barkhouse & Yee 2004;Gladders & Yee 2005;Miller et al 2005;Voit 2005;Mei et al 2006aMei et al ,b, 2009Mei et al , 2012Koester et al 2007;Gilbank et al 2008Gilbank et al , 2011Lidman et al 2008;Wilson et al 2009;Lin et al 2012). There is, however, some observational evidence for ongoing star formation in clusters at z 1, (e.g.…”

Dynamical analysis of the cluster pair: A3407 + A3408

“…They are the largest gravitationally bound systems in the universe, constraining both structure formation and the composition of the universe (e.g. Voit 2005;Allen et al 2011;Kravtsov & Borgani 2012). These systems also constitute important environments for the study of galaxy formation and evolution.…”