The evolution of dual AGN across cosmic time

Dual active galactic nuclei (gravitationally unbound pairs of AGN in a single galaxy or merging galaxy system) represent an observable connection between galaxy evolution and black hole growth, and they play an important role from merging galaxies to gravitational-wave-emitting binary systems. Despite this, there exists no systematic study of the evolution of dual AGN across cosmic time. Further, observational constraints on the dual AGN fraction in the nearby universe have been found to be higher than those predicted from simulations, resulting in inconsistent dual AGN rates predicted for z ≥ 1. Yet, an accurate measurement of the rate and evolution of dual AGN at all redshifts will inform us of the importance of feedback (or lack thereof) in merging galaxy systems and the role galaxy mergers play in triggering AGN. We are currently carrying out the first analysis to measure the dual AGN fraction at both high redshift, and as a a function of redshift, via a large (>700 AGN) and uniform study of dual AGN in galaxies, up to z = 3.5. By analyzing available data in wide and deep public Chandra surveys, we have placed the first constrained measurement of the dual AGN fraction at both the high-redshift (2.5 < z < 3.5) and low-redshift (z < 0.03) regime. Our results from our high-redshift sample allows for a better understanding of dual AGN activity during the peak time of galactic mergers, while our results from our nearby sample have important implications for the expected signal of the gravitational-wave background expected to be detected by pulsar timing arrays. Together, they represent the first projected measurement of the evolution of dual AGN activity over cosmic time.