A Spectroscopic Survey of Faint Quasars in the SDSS Deep Stripe. I. Preliminary Results from the Co-added Catalog

In this paper we present the first results of a deep spectroscopic survey of faint quasars in the Sloan Digital Sky Survey (SDSS) Southern Survey, a deep survey carried out by repeatedly imaging a 270 deg² area. Quasar candidates were selected from the deep data with good completeness over 0<z<5 and 2-3 mag fainter than the SDSS main survey. Spectroscopic follow-up was carried out on the 6.5 m MMT with Hectospec. The preliminary sample of this SDSS faint quasar survey (SFQS) covers ~3.9 deg², contains 414 quasars, and reaches g=22.5. The overall selection efficiency is ~66% (~80% at g<21.5) the efficiency in the most difficult redshift range (2<z<3) is better than 40%. We use the 1/V_a method to derive a binned estimate of the quasar luminosity function (QLF) and model the QLF using maximum likelihood analysis. The best model fits confirm previous results showing that the QLF has steep slopes at the bright end and much flatter slopes (-1.25 at z<~2.0 and -1.55 at z>~2.0) at the faint end, indicating a break in the QLF slope. Using a luminosity-dependent density evolution model, we find that the quasar density at M_g<-22.5 peaks at z~2, which is later in cosmic time than the peak of z~2.5 found from surveys of more luminous objects. The SFQS QLF is consistent with the results of the 2dF QSO Redshift Survey, the SDSS, and the 2dF-SDSS LRG and QSO Survey, but probes fainter quasars. We plan to obtain more quasars from future observations and establish a complete faint quasar sample with more than 1000 objects over 10 deg².

Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona.