A Deep Chandra Observation of the AGN Outburst and Merger in Hickson Compact Group 62

TL;DR

This study uses deep Chandra X-ray observations of galaxy group HCG 62 to analyze AGN-driven cavities, revealing low radiative power, the need for additional pressure sources, and evidence of a recent merger.

Contribution

The paper provides new constraints on cavity contents, detects X-ray emission from the central AGN for the first time, and identifies signs of a recent merger in HCG 62.

Findings

AGN outburst has extremely low radiative to mechanical power ratio

Cavities require additional pressure support from heavy particles or hot gas

Evidence of a recent merger in the galaxy group's IGM

Abstract

We report on an analysis of new Chandra data of the galaxy group HCG 62, well known for possessing cavities in its intragroup medium (IGM) that were inflated by the radio lobes of its central active galactic nucleus (AGN). With the new data, a factor of three deeper than previous Chandra data, we re-examine the energetics of the cavities and determine new constraints on their contents. We confirm that the ratio of radiative to mechanical power of the AGN outburst that created the cavities is less than 10^-4, among the lowest of any known cavity system, implying that the relativistic electrons in the lobes can supply only a tiny fraction of the pressure required to support the cavities. This finding implies additional pressure support in the lobes from heavy particles (e.g., protons) or thermal gas. Using spectral fits to emission in the cavities, we constrain any such volume-filling thermal gas to have a temperature kT > 4.3 keV. For the first time, we detect X-ray emission from the central AGN, with a luminosity of L(2-10 keV) = (1.1 +/- 0.4) x 10^39 erg s^-1 and properties typical of a low-luminosity AGN. Lastly, we report evidence for a recent merger from the surface brightness, temperature, and metallicity structure of the IGM.