- ph . C O ] 2 6 M ay 2 00 9 A SURVEY OF z ∼ 6 QUASARS IN THE SDSS DEEP STRIPE . II . DISCOVERY OF SIX

We present the discovery of six new quasars at z ∼ 6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about two magnitudes fainter than the luminous z ∼ 6 quasars found in the SDSS main survey and one magnitude fainter than the quasars reported in Paper I (Jiang et al. 2008). Four of them comprise a complete flux-limited sample at 21 < zAB < 21.8 over an effective area of 195 deg2. The other two quasars are fainter than zAB = 22 and are not part of the complete sample. The quasar luminosity function at z ∼ 6 is well described as a single power law Φ(L1450) ∝ L β 1450 over the luminosity range −28 < M1450 < −25. The best-fitting slope β varies from –2.6 to –3.1, depending on the quasar samples used, with a statistical error of 0.3–0.4. About 40% of the quasars discovered in the SDSS southern survey have very narrow Lyα emission lines, which may indicate small black hole masses and high Eddington luminosity ratios, and therefore short black hole growth time scales for these faint quasars at early epochs. Subject headings: cosmology: observations — quasars: general — quasars: emission lines Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 Apache Point Observatory, B.P Box 59, Sunspot, NM 88359 Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802