Abstract

The masses of supermassive black holes (SMBHs) in high-redshift quasars are commonly estimated using virial mass estimations calibrated on active galactic nuclei (AGN) in the local universe. However, when applied to new James Webb Space Telescope (JWST) observations at high redshift, these methods often yield SMBH masses that exceed theoretical growth limits, implying the need for heavy black hole seeds or periods of high mass accretion rates, also known as super-Eddington accretion. This tension highlights potential limitations of the virial approach at early cosmic times. This work investigates an alternative method for estimating high-redshift SMBH masses using the Broad Emission Line MApping Code (BELMAC) (Rosborough et al., 2024), a new forward-modeling, physics-based code that recovers SMBH masses through parameter estimation by directly modeling the broad line region rather than relying on virial scaling relations. Broad Hα lines are extracted from a sample of JWST spectra through spectral decomposition and modeled with BELMAC. The main goal is to determine whether BELMAC produces SMBH mass estimates that systematically differ from virial masses and reduce the need for extreme seeding or accretion scenarios. Results show that the BELMAC-derived masses for JADES-GN+189.20+62.18 are comparable to its virial estimate, while those for JADES-GN+189.27+62.19 and JADESGS+53.13-27.82 are systematically lower. However, the lower masses came from less robust fits than the comparable result and the +0.08 and -0.8 dex offsets from the virial masses were not significant, so heavy black hole seeds and/or periods of super-Eddington accretion remain the favored explanations. These comparisons provide insight into the reliability of current SMBH mass measurements and improve our understanding of SMBH growth in the early Universe.

Publication Date

7-2026

Document Type

Thesis

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (MS)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Andrew Robinson

Advisor/Committee Member

Manuela Campanelli

Advisor/Committee Member

Jeyhan Kartaltepe

Campus

RIT – Main Campus

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