A survey of z ∼ 6 Quasars in the sloan digital sky survey deep stripe. I. A flux-limited sample at zAB < 21

Linhua Jiang, Xiaohui Fan, James Annis, Robert H. Becker, Richard L. White, Kuenley Chiu, Huan Lin, Robert H. Lupton, Gordon T. Richards, Michael A. Strauss, Sebastian Jester, Donald P. Schneider

Research output: Contribution to journalArticlepeer-review

158 Scopus citations


We present the discovery of five quasars at z 6 selected from 260 deg 2 of the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The five quasars with 20 < zAB < 21 are 1-2 magnitudes fainter than the luminous z 6 quasars discovered in the SDSS main survey. One of them was independently discovered by the UKIRT Infrared Deep Sky Survey. These quasars, combined with another z 6 quasar known in this region, make a complete flux-limited quasar sample at zAB < 21. The sample spans the redshift range 5.85 ≤ z ≤ 6.12 and the luminosity range -26.5 ≤ M 1450 ≤ -25.4 (H 0 = 70 km s-1 Mpc -1, Ωm = 0.3, and ΩΛ = 0.7). We use the 1/Va method to determine that the comoving quasar spatial density at 〈z〉 = 6.0 and 〈M 1450〉 = -25.8 is (5.0 2.1) × 10-9 Mpc-3 mag-1. We model the bright-end quasar luminosity function (QLF) at z 6 as a power law Φ(L 1450) L β 1450. The slope β calculated from a combination of our sample and the luminous SDSS quasar sample is -3.1 0.4, significantly steeper than the slope of the QLF at z 4. Based on the derived QLF, we find that the quasar/active galactic nucleus (AGN) population cannot provide enough photons to ionize the intergalactic medium (IGM) at z 6 unless the IGM is very homogeneous and the luminosity (L*1450) at which the QLF power law breaks is very low.

Original languageEnglish (US)
Pages (from-to)1057-1066
Number of pages10
JournalAstronomical Journal
Issue number3
StatePublished - Mar 1 2008

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: active
  • Quasars: emission lines
  • Quasars: general


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