Effects of Galaxy Formation on Thermodynamics of the Intracluster Medium

Abstract

We present detailed comparisons of the intracluster medium (ICM) in\ncosmological Eulerian cluster simulations with deep Chandra observations of\nnearby relaxed clusters. To assess the impact of galaxy formation, we compare\ntwo sets of simulations, one performed in the non-radiative regime and another\nwith radiative cooling and several physical processes critical to various\naspects of galaxy formation: star formation, metal enrichment and stellar\nfeedback. We show that the observed ICM properties outside cluster cores are\nwell-reproduced in the simulations that include cooling and star formation,\nwhile the non-radiative simulations predict an overall shape of the ICM\nprofiles inconsistent with observations. In particular, we find that the ICM\nentropy in our runs with cooling is enhanced to the observed levels at radii as\nlarge as half of the virial radius. We also find that outside cluster cores\nentropy scaling with the mean ICM temperature in both simulations and Chandra\nobservations is consistent with being self-similar within current error bars.\nWe find that the pressure profiles of simulated clusters are also close to\nself-similar and exhibit little cluster-to-cluster scatter. The X-ray\nobservable-total mass relations for our simulated sample agree with the Chandra\nmeasurements to \\~10%-20% in normalization. We show that this systematic\ndifference could be caused by the subsonic gas motions, unaccounted for in\nX-ray hydrostatic mass estimates. The much improved agreement of simulations\nand observations in the ICM profiles and scaling relations is encouraging and\nthe existence of tight relations of X-ray observables, such as Yx, and total\ncluster mass and the simple redshift evolution of these relations hold promise\nfor the use of clusters as cosmological probes.\n