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Session 16 - QSOs and Active Galaxies.
Oral session, Monday, June 08

[16.03] HST Imaging of Quasar Host Galaxies Using NICMOS and WFPC2

M. J. Kukula (STScI), J. S. Dunlop, R. McLure (IfA, U. Edinburgh), C. P. O'Dea, S. A. Baum (STScI), L. Miller (U. Oxford)

The host galaxies of quasars and luminous AGN hold clues to several important questions about nuclear activity, including the triggering and fueling of the AGN, the origins of powerful radio sources, and the evolution of quasars with cosmological epoch. Because of the difficulties involved in detecting galaxies around faint quasars HST is the ideal instrument for this type of study, and several recent programs have successfully made use of its unique capabilities, often with surprising results.

The two ongoing HST programs described here use carefully matched samples of radio-loud and radio-quiet quasars (RLQs and RQQs) in order to avoid many of the problems of bias and sample incompatibility which have lead to confusion in the past. By careful choice of filters we also ensure that, regardless of redshift, we always observe longward of the 4000Åbreak in the galaxy's rest frame (where the galaxy:quasar luminosity ratio is more favorable) and that our images remain free from contamination by strong line emission which could mask the true distribution of the starlight.

The first program uses WFPC2 images to examine how the host galaxy R-band morphology and luminosity are related to the optical and radio luminosity of RLQs and RQQs with -23 > M_V > -26 in a narrow redshift range (0.1 < z < 0.3).

In the second program we use WFPC2 and NICMOS to trace the evolution of the hosts of RLQs and RQQs across four redshift bins from the present day back to the peak of the quasar era at z\simeq 2. In order to separate the effects of redshift from those of optical luminosity, we have confined our quasar samples to objects with a narrow range of absolute magnitudes centered on M_V = -24.5.

The preliminary results of both programs will be presented.

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