1 The Palomar - Quest ( PQ ) Survey : The Science Case

3.1 The Large QSO Survey. The principal effort of the Yale group is a search for QSOs using both colors and variability as selection criteria. Different combinations of UBRIriz colors can be used to select QSOs out to z ~ 6, with a majority at z ~ 2 ± 1. Variability is essentially redshift-independent selection method. For a demonstration of the methodology, see, e.g., Rengstorf et al. (2003). Over the survey area of 15,000 deg, we expect to detect ~ 300,000 QSOs down to our flux limits. We plan to obtain spectroscopic redshifts for ~ 1,000 of them, mainly to calibrate the selection functions and photometric redshifts (which we believe we can estimate from colors with a typical accuracy Δz ≈ 0.2). We note that many of the 2dFQz survey spectroscopically identified QSOs, as well as many QSOs from SDSS and other surveys will be within our area; we will make a full use of this external information. The resulting unprecedented QSO sample will be used for several projects, as follows: