Incidence of<i>WISE</i>-selected obscured AGNs in major mergers and interactions from the SDSS

Abstract

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