Galaxy interactions trigger rapid black hole growth: An unprecedented view from the Hyper Suprime-Cam survey

Collisions and interactions between gas-rich galaxies are thought to be pivotal stages in their formation and evolution, causing the rapid production of new stars, and possibly serving as amechanism for fueling supermassive black holes (BHs). Harnessing the exquisite spatial resolution (∼0.5) afforded by the first ∼170 deg² of the Hyper Suprime- Cam (HSC) survey, we present our new constraints on the importance of galaxy-galaxy major mergers (1 : 4) in growing BHs throughout the last ∼8Gyr. Utilizing mid-infrared observations in the WISE all-sky survey, we robustly select active galactic nuclei (AGN) and mass-matched control galaxy samples, totaling ∼140000 spectroscopically confirmed systems at i < 22 mag. We identify galaxy interaction signatures using a novel machine-learning random forest decision tree technique allowing us to select statistically significant samples of major mergers, minor mergers / irregular systems, and noninteracting galaxies. We use these samples to show that galaxies undergoing mergers are a factor of ∼2-7 more likely to contain luminous obscured AGN than non-interacting galaxies, and this is independent of both stellarmass and redshift to z < 0.9. Furthermore, based on our comparison of AGN fractions in mass-matched samples, we determine that themost luminous AGN population (LAGN ≳ 10⁴⁵ erg s^-1) systematically reside in merging systems over non-interacting galaxies. Our findings show that galaxy-galaxy interactions do, on average, trigger luminous AGN activity substantially more often than in secularly evolving non-interacting galaxies, and we further suggest that the BH growth rate may be closely tied to the dynamical time of the merger system.