Supermassive Blackhole Fueling in IllustrisTNG: Impact of environment

The connection between galaxy mergers and AGN activity is a subject of considerable debate. It involves two broad questions: 1) Do mergers trigger AGN activity? 2) What is their relative contribution to driving AGN activity and BH growth, compared to secular processes? I will present recent results on the AGN properties of supermassive black hole (BH) systems (pairs, triples and higher order multiples) in the IllustrisTNG (TNG100) universe. These systems are precursors to gravitationally bound BH binaries which are expected to be detected by LISA. We find enhanced AGN activity (by factors of up to a few) in BH systems on scales less than 0.1 Mpc/h. We also find that the abundance of dual AGNs in TNG100 is consistent with the observed ultra hard X-ray AGN samples. On larger spatial scales (~1 Mpc), however, no significant enhancements in AGN activity are associated with BH pairs and multiples, even at high Eddington ratios. The enhancement of AGN activity in rich, small-scale (~0.1 h−1 Mpc) environments is therefore likely to be driven by galaxy interactions and mergers. Nonetheless, the overall percentage of AGN that live in ~0.1 h−1 Mpc scale multiples is still subdominant. Thus, our results support the existence of a merger-AGN connection, but they also suggest that mergers and interactions play a relatively minor role in fueling the AGN population as a whole.