Incidence of WISE-Selected Obscured AGNs in Major Mergers and Interactions from the SDSS

TL;DR

This study demonstrates a significant increase in dust-obscured AGNs in major galaxy mergers using WISE and SDSS data, highlighting the importance of infrared observations in understanding AGN activity during galaxy interactions.

Contribution

It introduces a new volume-limited catalog of major mergers and interactions, revealing the strong link between dust-obscured AGNs and galaxy merging, which was previously underappreciated.

Findings

Major mergers are 5-17 times more likely to host dusty AGNs.

One-quarter of Seyferts show colors indicative of dusty AGNs.

AGNs are five times more likely to be obscured in merging galaxies.

Abstract

We use the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS) to confirm a connection between dust-obscured active galactic nuclei (AGNs) and galaxy merging. Using a new, volume-limited (z <= 0.08) catalog of visually-selected major mergers and galaxy-galaxy interactions from the SDSS, with stellar masses above 2x10^10 Msun, we find that major mergers (interactions) are 5-17 (3-5) times more likely to have red [3.4]-[4.6] colors associated with dust-obscured or `dusty' AGNs, compared to non-merging galaxies with similar masses. Using published fiber spectral diagnostics, we map the [3.4]-[4.6] versus [4.6]-[12] colors of different emission-line galaxies and find one-quarter of Seyferts have colors indicative of a dusty AGN. We find that AGNs are five times more likely to be obscured when hosted by a merging galaxy, half of AGNs hosted by a merger are dusty, and we find no enhanced frequency of optical AGNs in merging over non-merging galaxies. We conclude that undetected AGNs missed at shorter wavelengths are at the heart of the ongoing AGN-merger connection debate. The vast majority of mergers hosting dusty AGNs are star-forming and located at the centers of Mhalo<10^13 Msun groups. Assuming plausibly short duration dusty-AGN phases, we speculate that a large fraction of gas-rich mergers experience a brief obscured AGN phase, in agreement with the strong connection between central star formation and black hole growth seen in merger simulations.