Discovering and Harnessing Galactic Correlates of Supermassive Black Hole Growth

The co-evolution of supermassive black holes (SMBHs) and galaxies can be effectively constrained through sample-based analyses of the galactic correlates of long-term SMBH growth. Relevant correlates include stellar mass (M*), star formation rate (SFR), and compactness. The sample-averaged SMBH accretion rate (BHAR), which constrains long-term SMBH growth in galaxy populations of interest, is measured using Chandra, XMM-Newton, and eROSITA surveys data covering the standard "wedding-cake" design in sensitivity vs. solid-angle discovery space - including the Chandra Deep Fields, XMM-SERVS, COSMOS, and eFEDS. We have been advancing such investigations using partial-correlation analyses and complete, high-quality samples now reaching 8100 AGNs in 1.3 million galaxies, and I will briefly summarize some key findings. 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 BHAR-SFR correlation is observed, indicating synchronized 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. By combining these empirical results with large-scale simulations of galaxy evolution, we can trace SMBH growth through both accretion and mergers across cosmic history. Our work has clarified the evolution of the SMBH mass function, the SMBH mass versus galaxy stellar mass scaling relation, the relative importance of accretion and mergers to overall SMBH growth, and the marked decline in SMBH growth since z ~ 2. Such studies will soon be substantially extended by combining the massive Chandra, XMM-Newton, and eROSITA archives with surveys by, e.g., Rubin, Euclid, Roman, Xuntian, and new spectroscopic facilities.