AAS 207th Meeting, 8-12 January 2006
Session 149 AGN: Host Galaxies and Clustering
Oral, Wednesday, 10:00-11:30am, January 11, 2006, Salon 1

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[149.04] On the host galaxies of quasars

D.J.E. Floyd (STScI / ROE)

I present highlights from three distinct, but inter-connected studies of the nature and evolution of the host galaxies of quasars from z\approx 0.1-2

I first explore high-luminosity (MV<-25) quasars at low-redshift (z\approx 0.4) using HST, to study of the relationship between quasar / galaxy luminosity ratio and the black-hole / spheroid mass relation. Quasars with high nuclear-to-host luminosity ratios can be explained in terms of sub-Eddington accretion rates onto black holes in the high-mass tail of the black-hole:spheroid relation. The results imply that, owing to the Schechter function cutoff, host mass should not continue to increase linearly with quasar luminosity, at the very highest luminosities. Any quasars more luminous than MV = -27 should be found in massive elliptical hosts which at the present day would have MV ~-24.5.

In the second study I present HST U-V colours for host galaxies at z=1-2, to provide the first unbiased estimates of quasar host galaxy evolution out to cosmologically significant distances. Host galaxy colours are found to be broadly consistent with the assumption of passive evolution, with a small amount of ongoing star-formation. The differences between radio-loud and radio-quiet quasar hosts are discussed.

Finally, the same modelling technique is applied to a sample of ULIRG's and a control sample of IR-bright QSO's, matched in terms of their 60 \mum luminosity. Using UKIRT K-band imaging to detect the presence of any well-evolved stellar population, the possibility of an evolutionary link between ULIRG's and Quasars is explored.

I gratefully acknowledge funding from the Particle Physics and Astronomy Research Council, in the United Kingdom, and Space Telescope Science Institute, Baltimore, MD.

The author(s) of this abstract have provided an email address for comments about the abstract: floyd@stsci.edu

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