A Catalog of 220 Offset and Dual AGNs: Increased AGN Activation in Major Mergers and Separations under 4 kpc

TL;DR

This study presents a large catalog of 220 offset and dual AGNs observed by HST, revealing that AGN activity peaks at SMBH separations under 4 kpc, especially in major mergers, with no significant dependence on other galaxy properties.

Contribution

The paper introduces the ACS-AGN Merger Catalog and provides new empirical evidence on AGN activation related to SMBH separation and merger mass ratio.

Findings

AGN fraction peaks at SMBH separations under 4 kpc

AGNs are more common in major mergers

No correlation between AGN luminosity and merger properties

Abstract

During galaxy mergers, gas and dust is driven towards the centers of merging galaxies, triggering enhanced star formation and supermassive black hole (SMBH) growth. Theory predicts that this heightened activity peaks at SMBH separations $<$20 kpc; if sufficient material accretes onto one or both of the SMBHs for them to become observable as active galactic nuclei (AGNs) during this phase, they are known as offset and dual AGNs, respectively. To better study these systems, we have built the ACS-AGN Merger Catalog, a large catalog ($N=220$) of uniformly selected offset and dual AGN observed by $\textit{HST}$ at $0.2<z<2.5$ with separations $<$20 kpc. Using this catalog, we answer many questions regarding SMBH -- galaxy coevolution during mergers. First, we confirm predictions that the AGN fraction peaks at SMBH pair separations $<$10 kpc; specifically, we find that the fraction increases significantly at pair separations of $<$4 kpc. Second, we find that AGNs in mergers are preferentially found in major mergers and that the fraction of AGNs found in mergers follows a logarithmic relation, decreasing as merger mass ratio increases. Third, we do not find that mergers (nor the major or minor merger subpopulations) trigger the most luminous AGNs. Finally, we find that nuclear column density, AGN luminosity, and host galaxy star formation rate have no dependence on SMBH pair separation or merger mass ratio in these systems, nor do the distributions of these values differ significantly from that of the overall AGN population.