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

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 in the magnitude range −27.6 < M 1450 < −25.5. We determine the quasar comoving spatial density at = 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.

Citation

Myers, A. D., Wang, F., Yang, J., Fan, X., Wu, X., Yue, M., …Nunez, E. H. (2019). 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. Astrophysical Journal, 884(1), Article 30. https://doi.org/10.3847/1538-4357/ab2be5

• Journal Article Type: Article
• Acceptance Date: Jun 20, 2019
• Online Publication Date: Oct 8, 2019
• Publication Date: Oct 10, 2019
• Deposit Date: Oct 29, 2019
• Publicly Available Date: Oct 31, 2019
• Journal: Astrophysical Journal
• Print ISSN: 1538-4357
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 884
• Issue: 1
• Article Number: 30
• DOI: https://doi.org/10.3847/1538-4357/ab2be5
• Keywords: Early universe; Galaxies: active; Galaxies: high-redshift; Quasars
• Public URL: https://nottingham-repository.worktribe.com/output/2987443
• Publisher URL: https://iopscience.iop.org/article/10.3847/1538-4357/ab2be5
• Additional Information: Journal title: The Astrophysical Journal; Article type: paper; Article title: 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; Copyright information: © 2019. The American Astronomical Society. All rights reserved.; Date received: 2018-10-28; Date accepted: 2019-06-20; Online publication date: 2019-10-08