Uncovering the Signatures of Obscured AGN in Mergers

Galaxy mergers have long been implicated as drivers of supermassive black hole (BH) and galaxy co-evolution, but the relative importance of mergers for fueling active galactic nuclei (AGN) is still uncertain. In large part, the ongoing debate stems from strong selection effects that are inherent to empirical studies of the merger/AGN connection. The most luminous AGN are often obscured by dust in late-stage mergers; infrared (IR) and hard X-ray selected AGN are much more likely to be hosted in mergers than AGN selected at other wavelengths. Using numerical simulations with radiative transfer, we have modeled the evolution of mid-IR AGN signatures during mergers, focusing on color selection with the Wide-field Infrared Survey Explorer (WISE). We confirm that WISE color selection is very efficient at identifying luminous AGN but show that most AGN are missed with standard selection criteria, even in late-stage major
mergers. Nonetheless, we find that many mid-IR-selected AGN should contain unresolved BH pairs. I’ll describe some recent results from X-ray follow-up studies that support our findings. Finally, I will discuss the potential for the James Webb Space Telescope to reveal spatially-resolved signatures of merger-triggered AGN, opening a new window into some of the most rapidly-accreting BHs in the nearby Universe.