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

ABSTRACT:

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 < 0.6 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 in host galaxy morphologies and stellar population ages, which may be linked to the two major episodes of accretion predicted by numerical simulations.  I will also describe a method to measure the M-sigma relation in dust-obscured quasars.  Since the nuclei of these objects are embedded in dust, their host galaxies are mostly uncontaminated by the blue quasar continuum, making it possible to measure sigma from stellar absorption features at short wavelengths.  

 

At the same time, they show broad emission lines at longer wavelengths, from which black hole (BH) masses can be estimated by the virial method.  I will present results from a pilot sample of nine QSOs with redshifts 0.14 < z < 0.37. We find that there is an offset between the position of our objects and the local relation for AGN, in the sense that the majority of the red QSO hosts have lower velocity dispersions and/or more massive black holes than local galaxies. These results are in agreement with those from recent studies of Sy1 galaxies at similar and higher redshifts. This could indicate an unusually rapid growth in the host galaxies since z~0.2.   However, we find a striking trend with AGN luminosity that may indicate a bias in the M-sigma relation for the most luminous AGN.