Uplift, feedback and buoyancy: radio lobe dynamics in NGC 4472

Abstract

We present results from deep (380 ks) \textit{Chandra} observations of the AGN outburst in the massive early-type galaxy NGC 4472. We detect cavities in the gas coincident with the radio lobes and estimate the eastern and western lobe enthalpy to be $(1.1\pm 0.5)\times 10^{56}$ erg and $(3\pm 1)\times 10^{56}$ erg, and the average power required to inflate the lobes to be $(1.8\pm 0.9)\times 10^{41}$ erg s${}^{-1}$ and $(6\pm 3)\times 10^{41}$ erg s${}^{-1}$, respectively. We also detect enhanced X-ray rims around the radio lobes with sharp surface brightness discontinuities between the shells and the ambient gas. The temperature of the gas in the shells is less than that of the ambient medium, suggesting that they are not AGN-driven shocks but rather gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to be up to $(1.1\pm 0.3)\times 10^{56}$ erg and $(3\pm 1)\times 10^{56}$ erg for the eastern and western rim respectively, constituting a significant fraction of the total outburst energy. A more conservative estimate suggests that the gas in the rim was uplifted a smaller distance, requiring only $20-25\%$ of this energy. In either case, if a significant fraction of this uplift energy is thermalized via hydrodynamic instabilities or thermal conduction, our results suggest that it could be an important source of heating in cool core clusters and groups. We also find evidence for a central abundance drop in NGC 4472. The iron abundance profile shows that the region along the cavity system has a lower metallicity than the surrounding, undisturbed gas, similar to the central region. This also shows that bubbles have lifted low-metallicity gas from the center.

12 pages, 7 figures, accepted for publication in ApJ

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