A Morphological and Multicolor Survey for Faint QSO[CLC]s[/CLC] in the Groth-Westphal Strip

Quasars representative of the populous faint end of the luminosity functionare frustratingly dim with m~24 at intermediate redshift; moreover groundbasedsurveys for such faint QSOs suffer substantial morphological contamination bycompact galaxies having similar colors. In order to establish a more reliableultrafaint QSO sample, we used the APO 3.5-m telescope to take deep groundbasedU-band CCD images in fields previously imaged in V,I with WFPC2/HST. Ourapproach hence combines multicolor photometry with the 0.1" spatial resolutionof HST, to establish a morphological and multicolor survey for QSOs extendingabout 2 magnitudes fainter than most extant groundbased surveys. We presentresults for the "Groth-Westphal Strip", in which we identify 10 high likelihoodUV-excess candidates having stellar or stellar-nucleus+galaxy morphology inWFPC2. For m(606)<24.0 (roughly B<24.5) the surface density of such QSOcandidates is 420 (+180,-130) per square degree, or a surface density of 290(+160,-110) per square degree with an additional V-I cut that may furtherexclude compact emission line galaxies. Even pending confirming spectroscopy,the observed surface density of QSO candidates is already low enough to yieldinteresting comparisons: our measures agree extremely well with the predictionsof several recent luminosity function models.Comment: 29 pages including 6 tables and 7 figures. As accepted for publication in The Astronomical Journal (minor revisions