Cosmos Seminar
Apr
23
2026
Apr
23
2026
Description
Spectroscopic observations from JWST have uncovered a plethora of active galactic nuclei (AGN) at z>4 which appear to exhibit black hole (BH) mass (M_BH) to stellar mass (M∗) ratios significantly above the local relation when using standard virial mass recipes. However, stellar mass estimates of AGN hosts may be inaccurate due to limitations in traditional spectral energy distribution (SED) modeling techniques. In particular, previous studies typically do not fit emission lines in spectra, since most SED-fitting codes lack physically-motivated models of AGN emission. In this work, we fit NIRSpec/PRISM spectra of 40 broad-line AGN in the CEERS and RUBIES surveys at z~3.5-7 using the SED-fitting tool BEAGLE-AGN, which self-consistently models emission from the narrow-line region (NLR) of AGN. We quantify the effect of including various model components on derived M∗ measurements and expand the number of AGN with spectroscopic M∗ in this redshift range by ~40%. Leveraging this extensive sample, we explore M_BH/M∗ as a function of redshift and find that AGN at z<4 have ratios consistent with the local relation while those at z>4.5 appear to host significantly overmassive BHs, indicating that a rapid transition occurs between z~4-4.5 (a period of ~500 Myr). This evolution is consistent with some theoretical BH growth models; however, we cannot yet rule out the possibility that observational biases and systematic uncertainties may be at least partially responsible for this trend. Nonetheless, the rapid nature of this observed evolution merits further exploration, with significant implications for AGN-host galaxy coevolution throughout cosmic time.
Other Events in This Series
Jan
23
2025
Cosmos Seminar: Seeking to Uncover The Obliquities of Small Planets
Jack Lubin is a postdoctoral researcher in Astrophysics at the University of California, Los Angeles
3:30 pm – 4:30 pm • In Person
Speaker(s): Jack Lubin - UCLA
Mar
13
2025
Cosmos Seminar
Cosmos Seminar
3:30 pm – 4:30 pm • In Person
Speaker(s): William Roper - University of Sussex and Stephen Wilkins - University of Sussex