Quasar Black Hole Masses and Triggering Mechanisms: A Study Based on Low Redshift Host Galaxies

Gabriela Canalizo
The University of California, Riverside

Recent observations of low redshift quasar host galaxies indicate that mergers and significant episodes of star formation are ubiquitous in these galaxies. By constraining the timescales of such events we can gain a better understanding of the role of AGN feedback in galaxy evolution. I will discuss results from a long campaign of space- and ground-based imaging and spectroscopic observations of z < 0.5 hosts that imply that mergers are indeed essential for the triggering of quasars, and that these mergers invariably induce starbursts either during or shortly after the merger. There appears to be, however, a large range of values for the time delays between the merger and the onset of the nuclear activity, varying from a few Myr to more than a Gyr. We find some evidence for a bimodal distribution, although this could be a selection effect. I will also present results from our first attempt to measure the relation relation between black hole mass and velocity dispersions in quasars. The use of this correlation in quasars is hampered by the difficulty in measuring sigma in host galaxies that tend to be overpowered by their bright nuclei. I will discuss a project that focuses on z~0.3 quasars suffering from heavy extinction at shorter wavelengths. This makes it possible to obtain clean spectra of the hosts in the spectral regions of interest, while broad lines (like H-alpha) are still visible at longer wavelengths. We compare black hole masses obtained from velocity dispersions to those obtained from the BLR and thus probe the evolution of this relation and black hole growth with redshift and luminosity.