A Census of WISE-selected Dual and Offset AGN Across the Sky: New Constraints on Merger-Driven Triggering of Obscured AGN

Abstract: Pairs of galaxies hosting active galactic nuclei (AGN) are powerful probes of merger-driven supermassive black hole (SMBH) growth as they can resolve individual AGN and trace mergers over a large range of physical separations. To exploit this on a large scale for the first time for both obscured and unobscured AGN, we use photometric redshifts of AGN selected by the Wide-field Infrared Survey Explorer (WISE) to find probabilistic pairs (<100 kpc separations) across the sky, along with a comparison sample of inactive galaxy pairs. Our final sample of integrated pair probabilities yields 198 AGN-AGN pairs (dual AGN) and 2767 AGN-galaxy pairs (offset AGN) with uniformly measured AGN and host galaxy physical properties. We find the fraction of galaxy pairs hosting WISE AGN is dominated by offset AGN and significantly elevated above that of inactive galaxies for large host stellar masses. We show how the AGN merger fraction directly increases with AGN extinction for both offset and dual AGN, with up to ~40% of heavily obscured AGN found in galaxy pairs. Elevated AGN merger fractions coincide with increased host specific star formation rates that suggest merger-driven co-evolution of galaxies and SMBHs. Among dual AGN, the most rapid SMBH growth may occur within the less massive galaxy. Relative to stochastic mechanisms, mergers produce an excess of AGN at increasingly smaller separations, especially for obscured AGN (up to a factor of ~5), and augmented by correlated triggering. Finally, this excess is stronger than for lower luminosity optically-selected AGN, regardless of AGN obscuration level.