Sabrina Berger (The University of Melbourne)

Title: Simulations Meet JWST to Understand AGN at Cosmic Dawn
Abstract: The James Webb Space Telescope (JWST) is transforming our understanding of active galactic nuclei (AGN) in the early Universe. For the first time, astronomers have detected and characterized galaxies hosting luminous quasars at z > 6. JWST has also uncovered a population of compact, red objects—dubbed Little Red Dots (LRDs)—with unclear origins. One possibility is that these sources are AGN in the early stages of rapid black hole growth, potentially representing the seeds of quasars. Initial stellar mass estimates suggest black hole to stellar mass ratios much higher than in the local Universe, implying that early black holes may be overmassive. However, these measurements are limited by uncertainties in deriving physical properties from observations. We develop a Bayesian framework, informed by hydrodynamical simulations, to estimate systematic errors in high-z quasar host mass measurements and to begin to assess biases in interpretations of LRDs. We find that high-z quasar host masses can generally be recovered, though they are sometimes misestimated and may further deviate from local relations. Accurately constraining these biases is critical for understanding AGN and host co-evolution and avoiding premature assumptions about the nature of early AGN.

Yang Sun (University of Arizona)​

Title: Co-Evolution of SMBH and Galaxies from z~6 to the Present Day
Abstract: The relationship between a galaxy's stellar mass and its central supermassive black hole (SMBH) mass reflects the coevolution of SMBHs and their host galaxies. Studying the redshift evolution of this relationship offers key insights into the mechanisms driving the growth of SMBHs and their host galaxies. In the pre-JWST era, the studies of the MBH-M* relation evolution only reached to z~2 and the results remains controversial. Moreover, the newly discovered “overmassive” AGNs by JWST data show that substantial evolution may happen at z > 4, which, if true, will put new pieces of information on the timeline of the growth of SMBH and galaxy. In this talk, I will first introduce our critical determination of the MBH-M* relation at 1<z<4 using broad-NIR line AGN selected from JWST CONGRESS and FRESCO grism survey. We conclude that there is no compelling evidence for the evolution of the mass scaling relation up to z=4 at the high-mass end, after comprehensively modeling the selection biases using Monte Carlo methods. Then I will present our recent comprehensive studies of the mass scaling relation extended to 4<z<6 using both the low-mass BL AGNs and high-mass quasars discovered by JWST. We find that a significant increase in BH-to-stellar mass ratio is still present for low-mass AGNs, but not necessarily for quasars. Finally, I will then talk about the different behaviors of the mass scaling relation at the low- and high-mass regimes and the inferred potential growth pathway of those overmassive AGNs.