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

By Y. Matsuoka, M. Strauss, N. Kashikawa, M. Onoue, K. Iwasawa, Ji-Jia Tang, Chien-Hsiu Lee, M. Imanishi, Tohru Nagao, M. Akiyama and 37 more. Astrophysical Journal, 2018

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We present new measurements of the quasar luminosity function (LF) at z ∼ 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity M1450 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 < M1450 < −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.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

The bolometric quasar luminosity function at z = 0–7 (2020, background): “…compilation, we include measurements from Fontanot et al. (2007); Croom et al. (2009); Shen & Kelly (2012); Jiang et al. (2016); Palanque-Delabrouille et al. (2016); Yang et al. (2016); Akiyama et al. (2018); Matsuoka et al. (2018); McGreer et al. (2018); Wang et al. (2018a); Yang et al. (2018).”
A Census of Photometrically Selected Little Red Dots at 4 < z < 9 in JWST Blank Fields (2024, methodology): “…and Morishita et al. (2020) find that the less-luminous red quasar population could be anywhere from 10 to 100 times more common at z ∼ 7 − 8, compared to quasars luminosity functions at z ∼ 6, constructed from ground-based datasets (e.g. Matsuoka et al. 2018; Kato et al. 2020; Niida et al. 2020).”
A JWST/NIRSpec First Census of Broad-line AGNs at z = 4–7: Detection of 10 Faint AGNs with M BH ∼ 106–108 M ⊙ and Their Host Galaxy Properties (2023, methodology): “Our selected AGNs are typically faint with a UV magnitude of − 22 ≲ M UV ≲ − 17 mag, much fainter than the low-luminosity quasars found in ground-based observations at similar redshifts (e.g., Akiyama et al. 2018; Niida et al. 2020; Matsuoka et al. 2018).”