Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy injection in the gas around a fading AGN

TL;DR

Deep Chandra X-ray observations reveal extended hot gas and a possible bubble around a fading AGN in IC 2497, indicating energy injection and feedback processes that influence the host galaxy's evolution.

Contribution

This study provides new evidence of a bubble inflated by a fading AGN, highlighting the role of mechanical feedback in galaxy evolution and the lifecycle analogy with X-ray binaries.

Findings

Detection of extended soft X-ray emission around the AGN.

Identification of a bubble or cavity suggesting energy injection.

Discussion of scenarios including AGN-driven bubbles and shocks.

Abstract

We present deep Chandra X-ray observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp and hosting a fading AGN. We find extended soft X-ray emission from hot gas around the low intrinsic luminosity (unobscured) AGN ($L_{\rm bol} \sim 10^{42}-10^{44}$ erg s$^{-1}$). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN ($\mbox{E$_{\rm bub}$} \sim 10^{54} - 10^{55}$ erg). A possible scenario is that this bubble is inflated by the fading AGN, which after changing accretion state is now in a kinetic mode. Other possibilities are that the bubble has been inflated by the past luminous quasar ($L_{\rm bol} \sim 10^{46}$ erg s$^{-1}$), or that the temperature gradient is an indication of a shock front from a superwind driven by the AGN. We discuss the possible scenarios and the implications for the AGN-host galaxy interaction, as well as an analogy between AGN and X-ray binaries lifecycles. We conclude that the AGN could inject mechanical energy into the host galaxy at the end of its lifecycle, and thus provide a source for mechanical feedback, in a similar way as observed for X-ray binaries.