Properties of the Hot Ambient Medium of Early-type Galaxies Hosting Powerful Radio Sources

Abstract

We present an archival analysis of Chandra X-ray observations for twelve nearby early-type galaxies hosting radio sources with radio power $>10^{23}\mathrm{W}{\mathrm{Hz}}^{-1}$ at 1.4 GHz, similar to the radio power of the radio source in NGC 4261. Previously, in a similar analysis of eight nearby X-ray and optically-bright elliptical galaxies, Werner et al. 2012, found that NGC 4261 exhibited unusually low central gas entropy compared to the full sample. In the central 0.3 kpc of NGC 4261, the ratio of cooling time to freefall time ($t_{\mathrm{cool}}/t_{\mathrm{ff}}$) is less than $10$, indicating that cold clouds may be precipitating out of the hot ambient medium and providing fuel for accretion in the central region. NGC 4261 also hosts the most powerful radio source in the original sample. Because NGC 4261 may represent an important phase during which powerful feedback from a central active galactic nucleus (AGN) is fueled by multiphase condensation in the central kpc, we searched the Chandra archive for analogs to NGC 4261. We present entropy profiles of those galaxies as well as profiles of $t_{\mathrm{cool}}/t_{\mathrm{ff}}$. We find that one of them, IC 4296, exhibits properties similar to NGC 4261, including the presence of only single phase gas outside of $r\sim 2$ kpc and a similar central velocity dispersion. We compare the properties of NGC 4261 and IC 4296 to hydrodynamic simulations of AGN feedback fueled by precipitation. Over the course of those simulations, the single phase galaxy has an entropy gradient that remains similar to the entropy profiles inferred from our observations.

13 pages, 5 Figures, revised version of paper submitted to ApJ

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