The Final SDSS High-redshift Quasar Sample of 52 Quasars at z>5.7
Abstract
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\lt z≤slant 6.4, including 29 quasars with {z}{AB}≤slant 20 mag selected from 11,240 deg2 of the SDSS single-epoch imaging survey (the main survey), 10 quasars with 20≤slant {z}{AB}≤slant 20.5 selected from 4223 deg2 of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to {z}{AB}≈ 22 mag from the 277 deg2 in Stripe 82. They span a wide luminosity range of -29.0≤slant {M}1450≤slant -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 ({M}1450≥slant -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 low-luminosity quasars, the faint-end slope α and the characteristic magnitude {M}1450* are less well constrained, with α =-{1.90}-0.44+0.58 and {M}* =-{25.2}-3.8+1.2 mag. The spatial density of luminous quasars, parametrized as ρ ({M}1450\lt -26,z)=ρ (z=6){10}k(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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2016
- DOI:
- 10.3847/1538-4357/833/2/222
- arXiv:
- arXiv:1610.05369
- Bibcode:
- 2016ApJ...833..222J
- Keywords:
-
- galaxies: active;
- galaxies: high-redshift;
- quasars: emission lines;
- quasars: general;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 20 pages, 12 figures, Accepted for publication in The Astrophysical Journal