Galaxies and Cosmology Seminar: Physical Pathways for JWST-Observed Supermassive Black Holes in the Early Universe

Physical Pathways for JWST-Observed Supermassive Black Holes in the Early Universe

Observations with the James Webb Space Telescope (JWST) have identified an abundant population of supermassive black holes (SMBHs) already in place during the first few hundred million years of cosmic history. Most of them appear overmassive relative to the stellar mass in their host systems, challenging models of early black hole seeding and growth. Multiple pathways exist to explain their formation, including heavy seeds formed from direct collapse/supermassive stars or sustained super-Eddington accretion onto light stellar remnant seeds. We first use the cosmological simulation code GIZMO to study the formation and growth of DCBH seeds in the early Universe to explain the individual massive SMBHs. To grow the DCBHs, we implement a gas swallowing model set to match the Eddington accretion rate as long as the nearby gaseous environment, affected by stellar and accretion disk feedback, provides sufficient fuel. We find that to create massive AGN in overmassive systems at high redshifts, massive seeds accreting more efficiently than the fiducial Bondi-Hoyle model are needed. Next, we use the semi-analytical code A-SLOTH to predict the SMBH population and the emerging SMBH mass function from halo merger trees at increasingly high redshifts, to be compared with upcoming ultra-deep JWST surveys. We find that JWST will constrain the fraction of efficiently accreting (super-Eddington) SMBHs and possibly the existence of heavy seeds indirectly. Such observations will give insight to the process of SMBH evolution and environments during the emergence of the first galaxies.