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T. S. Hamilton (University of Pittsburgh), S. Casertano (Space Telescope Science Institute), D. A. Turnshek (University of Pittsburgh)
The results of an archival study of 71 medium-redshift QSOs observed with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope are presented. The QSOs have magnitudes MV \leq -23 mag (total nuclear+host light) and redshifts 0.06 \leq z \leq 0.46. For each object, the nuclear light component is subtracted, using two-dimensional image fits, and the luminosity and size of the underlying host galaxy are determined by fitting both an r1/4 and an exponential light profile, which represent a bulge and disk component, respectively.
A luminosity function which is not grossly affected by selection criteria is derived for the QSO host galaxies. This luminosity function is compared with that of normal galaxies, and a ratio of luminosity functions for QSO hosts and normal galaxies is derived. The logarithm of this ratio follows a nearly straight line when plotted against galaxy magnitude. The host luminosity function averages almost twice the luminosity of an MV* normal galaxy. The surface brightness distribution of the host galaxies is similar to the known relationship between the effective surface magnitude and size of Brightest Cluster Galaxies. This distribution is also examined in the context of radio-loudness and the merger history of the hosts.
Black hole masses for a subset of the QSOs are taken from the literature and used to calculate the Eddington limit for those objects. The ratio of nuclear luminosity to the Eddington limit decreases with black hole mass. Multi-parameter analyses are performed using Pricipal Components Analysis to search for underlying relationships among the host and nuclear variables. Among these results, a fundamental plane for QSOs is uncovered, analogous to that found for galaxies.
This work has been supported by funding from the Space Telescope Science Institute and the University of Pittsburgh.