The Co-evolution of black holes and galaxies

The growth of black holes appears to be closely connected with galaxy evolution, and yet how nuclear activity affects the growth of their host galaxies remains unclear. The main focus of this dissertation research is to systematically study the influence of nuclear activity on the growth of galaxies by examining the possible connection between AGN activity and star formation. By combining multi-wavelength photometry and spectroscopy, I characterize the properties of one of the largest samples of X-ray AGNs and their host galaxies up to z ∼ 3. To quantify the growth rate of black holes, I determine black hole masses (MBH) and Eddington ratios via the virial method using optical and near-IR spectroscopic observations. To derive AGN host galaxy properties, I develop a multi-component SED fitting technique which allows to disentangle the nuclear emission from the stellar light, and derive reliable physical properties, such as stellar masses (Mstellar) and star formation rates (SFRs). AGN host galaxies have, on average, SFRs that are consistent with those expected from normal star-forming galaxies with similar M stellar and redshift ranges, suggesting no clear evidence for enhanced or suppressed star formation. Furthermore, the MBH -Mstellar distribution for the majority of AGN host galaxies beyond the local universe is broadly consistent with the correlation that we observe today, indicating no significant evolution in the MBH - Mstellar relation. These results are in agreement with the observed lack of correlation between SFRs and AGN accretion, which can be explained by the AGN variability along with the broadly distributed Eddington ratios. I conclude that secular evolution may play an important role in growing both black holes and galaxies hosting moderate-luminosity AGNs at later cosmic time (z < 3).