Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6

Yoshiki Matsuoka, Michael A. Strauss, Nobunari Kashikawa, Masafusa Onoue, Kazushi Iwasawa, Ji Jia Tang, Chien Hsiu Lee, Masatoshi Imanishi, Tohru Nagao, Masayuki Akiyama, Naoko Asami, James Bosch, Hisanori Furusawa, Tomotsugu Goto, James E. Gunn, Yuichi Harikane, Hiroyuki Ikeda, Takuma Izumi, Toshihiro Kawaguchi, Nanako KatoSatoshi Kikuta, Kotaro Kohno, Yutaka Komiyama, Robert H. Lupton, Takeo Minezaki, Satoshi Miyazaki, Hitoshi Murayama, Mana Niida, Atsushi J. Nishizawa, Akatoki Noboriguchi, Masamune Oguri, Yoshiaki Ono, Masami Ouchi, Paul A. Price, Hiroaki Sameshima, Andreas Schulze, Hikari Shirakata, John D. Silverman, Naoshi Sugiyama, Philip J. Tait, Masahiro Takada, Tadafumi Takata, Masayuki Tanaka, Yoshiki Toba, Yousuke Utsumi, Shiang Yu Wang, Takuji Yamashita

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Abstract

We present new measurements of the quasar luminosity function (LF) at z ∼ 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity M 1450 from -30 to -22 mag. This is the fifth in a series of publications from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam Subaru Strategic Program survey. The LF was calculated with a complete sample of 110 quasars at 5.7 ≤ z ≤ 6.5, which includes 48 SHELLQs quasars discovered over 650 deg2 and 63 brighter quasars discovered by the Sloan Digital Sky Survey and the Canada-France-Hawaii Quasar Survey (including one overlapping object). This is the largest sample of z ∼ 6 quasars with a well-defined selection function constructed to date, which has allowed us to detect significant flattening of the LF at its faint end. A double power-law function fit to the sample yields a faint-end slope , a bright-end slope , a break magnitude , and a characteristic space density Gpc-3 mag-1. Integrating this best-fit model over the range -18 < M 1450 < -30 mag, quasars emit ionizing photons at the rate of s-1 Mpc-3 at z = 6.0. This is less than 10% of the critical rate necessary to keep the intergalactic medium ionized, which indicates that quasars are not a major contributor to cosmic reionization.

Original languageEnglish (US)
Article number150
JournalAstrophysical Journal
Volume869
Issue number2
DOIs
StatePublished - Dec 20 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • dark ages, reionization, first stars
  • galaxies: active
  • galaxies: high-redshift
  • intergalactic medium
  • quasars: general
  • quasars: supermassive black holes

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    Matsuoka, Y., Strauss, M. A., Kashikawa, N., Onoue, M., Iwasawa, K., Tang, J. J., Lee, C. H., Imanishi, M., Nagao, T., Akiyama, M., Asami, N., Bosch, J., Furusawa, H., Goto, T., Gunn, J. E., Harikane, Y., Ikeda, H., Izumi, T., Kawaguchi, T., ... Yamashita, T. (2018). Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6. Astrophysical Journal, 869(2), [150]. https://doi.org/10.3847/1538-4357/aaee7a