Investigating the evolution of the dual AGN system ESO~509-IG066

TL;DR

This study tracks the evolution of a dual AGN system in galaxy pair ESO 509-IG066, revealing a significant decrease in accretion activity in one nucleus and linking galaxy merger dynamics to black hole feeding processes.

Contribution

It provides multi-wavelength observational evidence of a dramatic change in accretion rate in one AGN and connects galaxy merger effects to black hole activity.

Findings

One AGN's flux decreased by a factor of 10 between 2004 and 2011.

Optical spectroscopy detected a broad H-alpha line, indicating ongoing accretion.

Merger dynamics influence gas kinematics near the black hole.

Abstract

We analyze the evolution of the dual AGN in ESO 509-IG066, a galaxy pair located at z=0.034 whose nuclei are separated by 11 kpc. Previous observations with XMM-Newton on this dual AGN found evidence for two moderately obscured ($N_H\sim10^{22}$ cm$^{-2}$) X-ray luminous ($L_X\sim10^{43}$ erg/s) nuclear sources. We present an analysis of subsequent Chandra, NuSTAR and Swift/XRT observations that show one source has dropped in flux by a factor of 10 between 2004 and 2011, which could be explained by either an increase in the absorbing column or an intrinsic fading of the central engine possibly due to a decrease in mass accretion. Both of these scenarios are predicted by galaxy merger simulations. The source which has dropped in flux is not detected by NuSTAR, which argues against absorption, unless it is extreme. However, new Keck/LRIS optical spectroscopy reveals a previously unreported broad H-alpha line which is highly unlikely to be visible under the extreme absorption scenario. We therefore conclude that the black hole in this nucleus has undergone a dramatic drop in accretion rate. From AO-assisted near-infrared integral-field spectroscopy of the other nucleus, we find evidence that the galaxy merger is having a direct effect on the kinematics of the gas close to the nucleus of the galaxy, providing a direct observational link between the galaxy merger and the mass accretion rate on to the black hole.