Physics and Astronomy PhD Thesis Defense - Chien-Ting Chen, Dartmouth College
Title: "The Growth of Supermassive Black Holes and Connections to Star Formation in Galaxies"
Location
Wilder 202
Sponsored by
Physics & Astronomy Department
Audience
Public
Abstract:A profound recent discovery in studies of the cosmic evolution ofgalaxies is that at the center of essentially every large galaxy there is a supermassive black hole (SMBH). This dissertation explores the origin of these massive black holes and their connection to the host galaxies, by studying rapidly growing black holes (the active galactic nuclei or AGNs) and galaxies that are actively forming stars using the wealth of observations in extragalactic surveys.
We first report a strong correlation between star formation rate (SFR) and the average SMBH accretion rate in star-forming galaxies. This highlights that even though the growth rates of the SMBHs and the host galaxies in individual galaxies hosting AGNs are not directly correlated potentially due to the short variability timescale of AGN relative to SF, averaging over the full AGN population still yields a strong linear correlation between AGN and star formation. We next present evidence for a link between AGN obscuration and host galaxy star formation in the most luminous AGNs: quasars. With careful decomposition of galaxy and AGN contributions through analysis of spectral energy distributions, we successfully placed constraints on the SFR in luminous quasars in which AGN radiation outshine the host galaxy at most wavelengths. We find that obscured quasars have ~2 times larger far-infrared (IR) detection fraction, far-IR flux and SFR than unobscured quasars. This result indicates that large-scale gas and dust in powerful star-forming galaxies contribute to obscuration of the AGN in luminous quasars.
Together, these two results support a scenario in which galaxy and SMBH grow from the same gas reservoir that can also obscures the central SMBH during the luminous quasar phase. Finally, we present a study of the correlation between the AGN mid-IR and X-ray luminositiesfor a large sample of spectroscopically confirmed type 1 quasars. We have determined that more luminous quasars show increasingly weak X-ray emission relative to their mid-IR luminosity, providing insight into the physics of quasar accretion and highlighting an important effect that must be accounted for in studies of SMBH evolution.
Location
Wilder 202
Sponsored by
Physics & Astronomy Department
Audience
Public
