What drives the growth of black holes?

Open Access
Yang, Guang
Graduate Program:
Astronomy and Astrophysics
Doctor of Philosophy
Document Type:
Date of Defense:
February 11, 2019
Committee Members:
  • William Nielsen Brandt, Dissertation Advisor/Co-Advisor
  • William Nielsen Brandt, Committee Chair/Co-Chair
  • Michael Eracleous, Committee Member
  • Donald P Schneider, Committee Member
  • Kohta Murase, Outside Member
  • Robin Bruce Ciardullo, Committee Member
  • X-ray
  • active galactic nucleus
  • black hole-galaxy coevolution
  • photometric redshift
  • AGN variability
  • extragalactic transient
There are supermassive black holes (SMBHs) in the centers of most massive galaxies. Observations of nearby systems have found that SMBH masses (M_BH ) are tightly correlated with host-galaxy properties such as bulge masses. These local SMBH-galaxy relations suggest that SMBH growth is fundamentally linked to host galaxies over cosmic history. Previous studies suggest that long-term average SMBH accretion rate (BHAR) is intrinsically related to star formation rate (SFR) for the overall galaxy population. However, we show that BHAR is more strongly correlated with host-galaxy stellar mass (M_*) rather than SFR (Chapter 2), and this BHAR-M_* relation does not depend on cosmic environment (Chapter 3). We further quantify this BHAR-M_* relation and its cosmic evolution at z = 0.4–4 (Chapter 4). However, we find this BHAR-M_* relation does not hold for bulge-dominated galaxies, and their BHAR primarily depends on SFR (Chapter 5). This BHAR-SFR relation among bulge-dominated galaxies indicates that SMBHs only coevolve with galactic bulges rather than the entire galaxies, consistent with the observations of the local universe. Aside from the content above, which centers on the theme of “what drives the growth of black holes”, this dissertation also includes my other three works as appendices. These works include studies of photometric redshift (Appendix A), X-ray variability of active galactic nuclei (Appendix B), and fast extragalactic X-ray transients (Appendix C).