X-ray Thermal Coronae of Galaxies in Hot Clusters — Ubiquity of Embedded Mini Cooling Cores

We present a systematic investigation of X-ray thermal coronae in 157 early-type galaxies and 22 late-type galaxies from a survey of 25 hot (kT > 3 keV), nearby (z < 0.05) clusters, based on Chandra archival data. Cool galactic coronae (kT = 0.5 1.1 keV generally) have been found to be very common, > 60% in NIR selected galaxies that are more luminous than 2 L∗, and > 40% in L∗ < LKs < 2 L∗ galaxies. These embedded coronae in hot clusters are generally smaller (1.5-4 kpc radii), less luminous ( < ∼ 10 erg s), and less massive (1010 M⊙) than coronae in poor environments, demonstrating the negative effects of hot cluster environments on galactic coronae. Nevertheless, these coronae still manage to survive ICM stripping, evaporation, rapid cooling, and powerful AGN outflows, making them a rich source of information about gas stripping, microscopic transport, and feedback processes in the cluster environment. Heat conduction across the boundary of the coronae has to be suppressed by a factor of > ∼ 100, which implies the X-ray gas in early-type galaxies is magnetized and the magnetic field plays an important role in energy transfer. Stripping through transport processes (viscosity or turbulence) also needs to be suppressed by at least a factor of ten at the coronal boundary. The stellar mass loss inside the corona is key to maintaining the gas balance in coronae. The luminous, embedded coronae, with high central density (0.1 0.4 cm), are mini-versions of group and cluster cooling cores. As the prevalence of coronae of massive galaxies implies a long lifetime ( > ∼ several Gyr), there must be a heat source inside coronae to offset cooling. While we argue that AGN heating may not generally be the heat source, we conclude that SN heating can be enough as long as the kinetic energy of SNe can be efficiently dissipated. We have also observed a connection between radiative cooling and the SMBH activity of their host galaxies as many coronae are associated with powerful radio galaxies. Cooling of the coronal gas may provide fuel for the central SMBH and nuclear star formation in environments where the amount of galactic cold gas is otherwise at a minimum. Diffuse thermal coronae have also been detected in at least 8 of 22 late-type (Sb or later) galaxies in our sample. Evidence for enhanced star formation triggered by the ICM pressure has been found in four late-type galaxies. The fraction of luminous X-ray AGN (> 10 ergs s) is not small (∼ 5%) in our sample. Subject headings: galaxies: clusters: general — X-rays: galaxies — galaxies: cooling flows — conduction — magnetic fields — radio sources: galaxies