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

TL;DR

This study analyzes the thermal structure of hot gas in 49 elliptical galaxies, exploring the connection between X-ray emitting gas, optical emission lines, and AGN feedback, highlighting the role of chaotic cold accretion.

Contribution

It provides new insights into the thermodynamic conditions associated with optical emission lines and their relation to AGN activity in elliptical galaxies.

Findings

Hα+[NII] emission correlates with higher densities and lower entropies.

No clear correlation between optical emission lines and global X-ray properties.

Possible weak positive correlation between AGN jet power and optical line luminosity.

Abstract

We present a study of the thermal structure of the hot X-ray emitting atmospheres for a sample of 49 nearby X-ray and optically bright elliptical galaxies using {\it 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, shorter cooling times, shallower entropy profiles, lower values of min($t_{\rm cool}/t_{\rm ff}$), and disturbed X-ray morphologies (linked to turbulent motions). However, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. The AGN jet powers of the galaxies with X-ray cavities show hint of a possible weak positive correlation with their 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.