Thermodynamic properties, multiphase gas, and AGN feedback in a large sample of giant ellipticals

We present a study of the thermal structure of the hot X-ray emitting atmospheres of a sample of 49 nearby X-ray and optically bright elliptical galaxies using Chandra X-ray data. We focus on the connection between the properties of the hot X-ray emitting gas and the cooler H$\alpha$+[NII] emitting phase, and the possible role of the latter in the AGN (Active Galactic Nuclei) feedback cycle. We do not find evident correlations between the H$\alpha$+[NII] emission and global properties such as X-ray luminosity, mass of hot gas, and gas mass fraction. We find that the presence of H$\alpha$+[NII] emission is more likely in systems with higher densities, lower entropies, shallower entropy profiles, lower values of min($t_{\rm cool}/t_{\rm ff}$), and disturbed X-ray morphologies which are tightly linked with the level of turbulent motions. However, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. We detected X-ray emitting central AGNs in 11 of the 25 H$\alpha$+[NII] emitting galaxies (~44%), and in only three of the 20 galaxies without any optical emission line nebulae. The AGN jet powers of the galaxies with X-ray cavities show hint of a possible weak positive correlation withtheir H$\alpha$+[NII] luminosities. This correlation and the observed trends in the thermodynamic properties may result from chaotic cold accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic simulations.