Galactic Correlates of Supermassive Black Hole Growth and Their Application

Supermassive black hole (SMBH) vs. galaxy co-evolution and SMBH feedback can be effectively constrained using sample-based studies of the galactic correlates of long-term SMBH growth. Relevant correlates include galaxy stellar mass (M_*), star-formation rate (SFR), and compactness. The sample-averaged SMBH accretion rate (BHAR) for galaxy populations of interest, constraining their long-term SMBH growth, is measured statistically using sensitive X-ray surveys data; e.g., from the Chandra Deep Fields, XMM-SERVS, COSMOS, and eFEDS. We have been advancing such investigations using partial-correlation analyses and new complete, superb-quality samples now reaching 8100 AGNs in 1.3 million galaxies, and I will briefly review some of our most important results. Specifically, (1) for the general galaxy population at z = 0.1-4, SMBH growth correlates most strongly with M_*; (2) for bulge-dominated systems, a strong linear BHAR-SFR correlation is found which indicates lockstep growth between SMBHs and bulges; (3) BHAR also clearly correlates with galaxy compactness among star-forming galaxies, likely due to enhanced nuclear gas density for compact galaxies. Furthermore, the combination of such empirical correlations with large-scale numerical simulations of galaxy evolution allows SMBH growth due to accretion and mergers to be quantitatively tracked over most of cosmic history, producing notable insights about the evolution of the SMBH mass function, the M_BH-M_* scaling relation, the relative importance of accretion vs. mergers to overall SMBH growth, and long-lived wandering SMBHs.