Linhua Jiang, Ian D. McGreer, Xiaohui Fan, Michael A. Strauss, Eduardo Bañados, Robert H. Becker, Fuyan Bian, Kara Farnsworth, Yue Shen, Feige Wang, Ran Wang, Shu Wang, Richard L. White, Jin Wu, Xue Bing Wu, Jinyi Yang, Qian Yang

Research output: Contribution to journalArticlepeer-review

239 Scopus citations


We present the discovery of nine quasars at z ∼ 6 identified in the Sloan Digital Sky Survey (SDSS) imaging data. This completes our survey of z ∼ 6 quasars in the SDSS footprint. Our final sample consists of 52 quasars at 5.7 < z ≤ 6.4, including 29 quasars with zAB ≤ 20 mag selected from 11,240 deg2 of the SDSS single-epoch imaging survey (the main survey), 10 quasars with 20 ≤ zAB ≤ 20.5 selected from 4223 deg2 of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to zAB ≈ 22 mag from the 277 deg2 in Stripe 82. They span a wide luminosity range of -29.0 ≤ M1450 ≤ -24.5. This well-defined sample is used to derive the quasar luminosity function (QLF) at z ∼ 6. After combining our SDSS sample with two faint (M1450 ≥ -23 mag) quasars from the literature, we obtain the parameters for a double power-law fit to the QLF. The bright-end slope β of the QLF is well constrained to be β = -2.8 ± 0.2. Due to the small number of lowluminosity quasars, the faint-end slope α and the characteristic magnitude M 1450 are less well constrained, with =α= -1.90 +0.58 -0.44 and M∗ = -25.2+1.2 -3.8mag. The spatial density of luminous quasars, parametrized as p(M1450<-26, z) = p(=6) 10k(z-6), drops rapidly from z ∼ 5 to 6, with k = -0.72 ± 0.11. Based on our fitted QLF and assuming an intergalactic medium (IGM) clumping factor of C=3, we find that the observed quasar population cannot provide enough photons to ionize the z ∼ 6 IGM at ∼90% confidence. Quasars may still provide a significant fraction of the required photons, although much larger samples of faint quasars are needed for more stringent constraints on the quasar contribution to reionization.

Original languageEnglish (US)
Article number222
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 20 2016


  • galaxies: active
  • galaxies: high-redshift
  • quasars: emission lines
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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