Cosmological Simulations of Galaxy Clusters

Abstract

We review recent progress in the description of the formation and evolution\nof galaxy clusters in a cosmological context by using numerical simulations. We\nfocus our presentation on the comparison between simulated and observed X-ray\nproperties, while we will also discuss numerical predictions on properties of\nthe galaxy population in clusters. Many of the salient observed properties of\nclusters, such as X-ray scaling relations, radial profiles of entropy and\ndensity of the intracluster gas, and radial distribution of galaxies are\nreproduced quite well. In particular, the outer regions of cluster at radii\nbeyond about 10 per cent of the virial radius are quite regular and exhibit\nscaling with mass remarkably close to that expected in the simplest case in\nwhich only the action of gravity determines the evolution of the intra-cluster\ngas. However, simulations generally fail at reproducing the observed cool-core\nstructure of clusters: simulated clusters generally exhibit a significant\nexcess of gas cooling in their central regions, which causes an overestimate of\nthe star formation and incorrect temperature and entropy profiles. The total\nbaryon fraction in clusters is below the mean universal value, by an amount\nwhich depends on the cluster-centric distance and the physics included in the\nsimulations, with interesting tensions between observed stellar and gas\nfractions in clusters and predictions of simulations. Besides their important\nimplications for the cosmological application of clusters, these puzzles also\npoint towards the important role played by additional physical processes,\nbeyond those already included in the simulations. We review the role played by\nthese processes, along with the difficulty for their implementation, and\ndiscuss the outlook for the future progress in numerical modeling of clusters.\n