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
Findlay, Joseph R.
Davies, Frederick B.
Farina, Emanuele P.
Hennawi, Joseph F.
McGreer, Ian D.
Lyke, Brad W.
Myers, Adam D.
Nunez, Evan Haze
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationFeige Wang et al 2019 ApJ 884 30
RightsCopyright © 2019. The American Astronomical Society. All rights reserved.
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AbstractThis 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 less than or similar to z less than or similar to 6.9 from an area of similar to 13,020 deg(2), and present the quasar luminosity function (QLF) at z similar to 6.7. The measured QLF follows Phi(L-1450) proportional to 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 similar to 6 to z similar to 6.7, corresponding to a rapid decline by a factor of similar to 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 similar to 3 and 5. We measured quasar comoving emissivity at z similar to 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 greater than or similar to 6.5 is measured to be greater than or similar to 22%. In addition, we also report the discovery of six additional quasars at z similar to 6 in the Appendix.
VersionFinal published version
SponsorsNational Key R&D Program of China [2016YFA0400703]; National Science Foundation of ChinaNational Natural Science Foundation of China [11533001, 11721303]; US NSF grantNational Science Foundation (NSF) [AST-1515115]; NASA ADAP grant [NNX17AF28G]; National Science Foundation through REU grant [AST-1560461]; NOAO program [GN-2018A-C-1]; ESO Programme [179.A-2010, 179.A-2004]; National Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); National Astronomical Observatories, Chinese Academy of SciencesChinese Academy of Sciences; Special Fund for Astronomy from the Ministry of Finance in China