Exploring Reionization-era Quasars. III. Discovery of 16 Quasars at 6.4 ≲ z ≲ 6.9 with DESI Legacy Imaging Surveys and the UKIRT Hemisphere Survey and Quasar Luminosity Function at z ∼ 6.7

Journal
Date Issued
2019
Author(s)
Wang, Feige
•
Yang, Jinyi
•
Fan, Xiaohui
•
Wu, Xue-Bing
•
Yue, Minghao
•
Li, Jiang-Tao
•
Bian, Fuyan
•
Jiang, Linhua
•
Bañados, Eduardo
•
Schindler, Jan-Torge
•
Findlay, Joseph R.
•
Davies, Frederick B.
•
•
Farina, Emanuele P.
•
Green, Richard
•
Hennawi, Joseph F.
•
Huang, Yun-Hsin
•
Mazzuccheli, Chiara
•
McGreer, Ian D.
•
Venemans, Bram
•
Walter, Fabian
•
Dye, Simon
•
Lyke, Brad W.
•
Myers, Adam D.
•
Haze Nunez, Evan
DOI
Abstract
This is the third paper in a series aimed at finding reionization-era quasars with the combination of DESI Legacy imaging Surveys (DELS), the Pan-STARRS1 (PS1) Survey, and near-infrared imaging surveys, such as the UKIRT Hemisphere Survey (UHS), as well as the Wide-field Infrared Survey Explorer (WISE) mid-infrared survey. In this paper, we describe the updated quasar candidate selection procedure, report the discovery of 16 quasars at 6.4 ≲ z ≲ 6.9 from an area of ∼13,020 deg2, and present the quasar luminosity function (QLF) at z ∼ 6.7. The measured QLF follows {{Φ }}({L}1450)\propto {L}1450-2.35 in the magnitude range -27.6 < M 1450 < -25.5. We determine the quasar comoving spatial density at < z> = 6.7 and M 1450 < -26.0 to be 0.39 ± 0.11 Gpc-3 and find the exponential density evolution parameter to be k = -0.78 ± 0.18 from z ∼ 6 to z ∼ 6.7, corresponding to a rapid decline by a factor of ∼6 per unit redshift toward earlier epochs. This indicates that the rapid decline of quasar spatial density at z > 5 that was found by previous works continues to z > 6, at a rate significantly faster than the average decline rate between z ∼ 3 and 5. We measured quasar comoving emissivity at z ∼ 6.7, which indicates that high-redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. The broad absorption line quasar fraction at z ≳ 6.5 is measured to be ≳22%. In addition, we also report the discovery of six additional quasars at z ∼ 6 in the Appendix.
Volume
884
Issue
1
Start page
30
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2019ApJ...884...30W
Rights
open.access
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