exploring reionization-era quasars III: Discovery of 16 quasars at 6.4 . z . 6.9 with desi legacy imaging surveys and ukirt hemisphere survey and quasar luminosity function at z ∼ 6.7

Feige Wang, Jinyi Yang, Xiaohui Fan, Xue Bing Wu, Minghao Yue, Jiang Tao Li, Fuyan Bian, Linhua Jiang, Eduardo Bañados, Jan Torge Schindler, Joseph R. Findlay, Frederick B. Davies, Roberto Decarli, Emanuele P. Farina, Richard Green, Joseph F. Hennawi, Yun Hsin Huang, Chiara Mazzuccheli, Ian D. McGreer, Bram VenemansFabian Walter, Simon Dye, Brad W. Lyke, Adam D. Myers, Evan Haze Nunez

Research output: Contribution to journalArticlepeer-review

Abstract

This is the third paper in a series aims at finding reionzation-era quasars with the combination of DESI Legacy imaging Surveys (DELS) and near-infrared imaging surveys, such as the UKIRT Hemisphere Survey (UHS), as well as the Wide-field Infrared Survey Explore (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 area of ∼13,020 deg2, and present the quasar luminosity function (QLF) at z ∼ 6.7. The measured QLF follows Φ(L1450) ∝ L14502.35 in the magnitude range –27.6< M1450 <–25.5. We determine the quasar comoving spatial density at hzi=6.7 and M1450 < −26.0 to be 0.39 ± 0.11Gpc3 and find that 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 towards earlier epoch, a rate significantly faster than that at z ∼ 3 − 5. The cosmic time between z ∼ 6 and z ∼ 6.7 is only 121 Myrs. The quasar density declined by a factor of more than three within such short time requires that SMBHs must grow rapidly or they are less radiatively efficient at higher redshifts. We measured quasar comoving emissivity at z ∼ 6.7 which indicate that high redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. The broad absorption line (BAL) quasar fraction at z & 6.5 is measured to be &22%. In addition, we also report the discovery of additional five quasars at z ∼ 6 in the appendix.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Oct 28 2018

Keywords

  • Cosmology: reionization
  • Galaxies: active
  • Galaxies: high-redshift
  • Quasars: general

ASJC Scopus subject areas

  • General

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