Optical variability of intermediate-mass black holes as a probe of black hole accretion and growth

Burke, Colin Jacob

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https://hdl.handle.net/2142/121408 Copy

Description

Title

Optical variability of intermediate-mass black holes as a probe of black hole accretion and growth

Author(s)

Burke, Colin Jacob

Issue Date

2023-06-02

Director of Research (if dissertation) or Advisor (if thesis)

Liu, Xin

Doctoral Committee Chair(s)

Shen, Yue

Committee Member(s)

• Gammie, Charles F
• Narayan, Gautham

Department of Study

Astronomy

Discipline

Astronomy

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• intermediate-mass black holes
• active galactic nuclei
• variability

Abstract

Active galactic nuclei (AGNs) in dwarf galaxies (dwarf AGNs) are believed to host accreting intermediate-mass black holes (IMBHs). The demographics of dwarf AGNs are an important tracer of supermassive black hole (SMBH) growth, because their relic IMBHs act as a fossil record of SMBH seeding pathways at high redshift. Being ubiquitous across wavelengths and timescales, AGN variability is useful for AGN identification and is an important probe of BH accretion. Because the physical timescales associated with BH accretion generally scale with the mass of the BH, dwarf AGNs with accreting IMBHs are new laboratories for studying BH accretion on human timescales. The first part of this dissertation is focused on observational evidence for a characteristic thermal timescale in accretion disks using optical light curves from stellar-mass accreting systems to SMBHs in AGNs. This is motivated by the ~ days timescale variability in the optical light curve of the dwarf AGN NGC 4395. These results are presented in Chapter 2. Chapter 3 focuses on identification of dwarf AGN from variability beyond z ~ 0.1 (the limit of what has been probed by previous work) using light curves from the Dark Energy Survey Supernova survey program. Chapter 4 presents a phenomenological forward model for forecasting dwarf AGNs and constraining the corresponding IMBH number density or occupation fraction with optical variability. Chapter 5 presents detailed spectroscopic tests of the AGN nature in a small sample of extremely metal-poor dwarf galaxies. Future test of BH-host galaxy co-evolution in the IMBH regime could help illuminate models of SMBH seeding and feedback in dwarf galaxies. Constraining the IMBH number density using these probes will be critical for forecasting the gravitational wave events with the upcoming Laser Interferometer Space Antenna (LISA) mission.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Colin J. Burke

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