Hot X-ray gas in galaxies, groups and clusters

I investigate several aspects of X-ray gas in galaxies, groups and clusters, all related to the fundamental problems of radiative cooling and AGN feedback. A sample of 14 relaxed clusters and groups are studied, with an emphasis on their temperature and entropy profiles. Three clusters with isothermal temperature distributions are discovered which also have isentropic gas cores and weaker central radio activity than other cooling core clusters. This suggests a connection between gas cooling and feedback from supermassive black holes. A comparison of entropy profiles shows that within 0.1 virial radii, group entropy profiles are flatter than those of hot clusters and those predicted from simulations involving only gravity. From 0.1 to 0.35 virial radius, the slope of the cluster entropy profiles is consistent with simulations. Interesting systems (e.g., a hot but X-ray faint group and an isothermal group with a very high gas density core) in the sample are also discussed.; I also present work on the X-ray coronae of galaxies in rich clusters, including detailed studies of coronae in A1367 and a small corona in NGC 1265. Cool X-ray coronae of early-type galaxies (0.5--1 keV), pressure confined in hot (>3 keV) clusters, are found to be common, although their properties have been significantly modified by the ICM environment. Despite the effects of gas stripping, ICM evaporation and AGN outbursts of the central SMBH, the survival of these small and vulnerable coronae puts interesting constraints on the physics of the interactions of the coronae. For example, transport processes (e.g., heat conduction) must be strongly suppressed, presumably by magnetic fields and the coronae must avoid disruption by energy output from the central AGN.