Diffuse Baryons in Cosmic Structures

Abstract

I review the processes that govern the amount and the thermal state of the hot plasma pervading clusters and groups of galaxies: the gravitational heating driven by the DM merging histories, the radiative cooling of baryons, and the energy fed back by SNe and by AGNs or quasars. I argue that the X-ray emissions and the entropy levels now observed from clusters to groups require the AGNs to contribute substantially to preheat the gas before it falls into clusters, and the quasars to blow some plasma out of groups and galaxies.