Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 7.0

Abstract

We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O III] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg 2 , surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N V λ1240 emission and resembles that Corresponding author: Yoshiki Matsuoka yk.matsuoka@cosmos.ehime-u.ac.jp of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus these objects may be composites of quasars and star-forming galaxies.

A Significantly Neutral Intergalactic Medium Around the Luminous z = 7 Quasar J0252–0503

“…Among the six public known z7 quasars, two objects already have had damping wing analyses performed (Bolton et al 2011;Mortlock et al 2011;Bosman & Becker 2015;Greig et al 2017Greig et al , 2019Bañados et al 2018;Davies et al 2018b;Ďurovčíková et al 2020). Two other quasars are too faint (M 1450 −25) for damping wing analyses with current facilities (Matsuoka et al 2019a(Matsuoka et al , 2019b, and another is a broad absorption line (BAL) quasar in which strong absorption precludes determination of the intrinsic quasar spectrum (Wang et al 2018). Thus, J0252-0503 is the only known bright, non-BAL quasar at z7 of which a damping wing analysis has not been performed yet.…”

“…The earliest luminous quasars, powered by billion solar-mass supermassive black holes (SMBHs), can be used not only to constrain the physics of SMBH accretion and the assembly of the first generation of massive galaxies in the early universe, but also to obtain critical information on the physical conditions of the intergalactic medium (IGM) during the epoch of reionization (EoR). Although more than 200 z>6 quasars have been found in the past few decades (e.g., Fan et al 2001;Willott et al 2010;Wu et al 2015;Bañados et al 2016;Jiang et al 2016;Matsuoka et al 2016;Wang et al 2016;Reed et al 2017), only several tens of them are at z>6.5 (e.g., Venemans et al 2015;Mazzucchelli et al 2017;Wang et al 2017Wang et al , 2019Reed et al 2019;Yang et al 2019) and just six are currently known at z>7 (Mortlock et al 2011;Bañados et al 2018;Wang et al 2018;Matsuoka et al 2019aMatsuoka et al , 2019bYang et al 2019). The limited number of known high-redshift quasars is due to the combination of a rapid decline of quasar spatial density toward higher redshifts (e.g., Wang et al 2019), the lack of deep wide-field near-infrared surveys, and the presence of a large number of contaminants from Galactic cool dwarf populations in the photometric quasar selection process.…”

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XIII. Large-scale Feedback and Star Formation in a Low-luminosity Quasar at z = 7.07 on the Local Black Hole to Host Mass Relation

“…Thus, z > 6 quasars, seen when the universe was less than a billion years old, are a unique beacon to study SMBH and galaxy formation. To date, more than 200 quasars with rest-frame ultraviolet (UV) magnitude M 1450  −22 mag are known at z > 5.7 (Inayoshi et al 2020), most of which were discovered by wide-field optical and near-infrared surveys (e.g., Bañados et al 2016;Fan et al 2001Fan et al , 2003Jiang et al 2016;Matsuoka et al 2016Matsuoka et al , 2018aMatsuoka et al , 2018bMatsuoka et al , 2019aWillott et al 2007Willott et al , 2010. The sample includes eight quasars at z > 7 (Mortlock et al 2011;Bañados et al 2018;Wang et al 2018Wang et al , 2021Yang et al 2019Yang et al , 2020Matsuoka et al 2019aMatsuoka et al , 2019b.…”

Enhanced X-Ray Emission from the Most Radio-powerful Quasar in the Universe’s First Billion Years

“…The evolution of supermassive black holes (SMBHs) in the early universe represents a challenge for modern cosmology, requiring significant, sustained growth from primordial seeds to explain the population of observed quasars in the first billion years of the universe (e.g., Inayoshi et al 2020). In the past decade, not only has the number of known members of this population expanded through large surveys (e.g., Bañados et al 2016;Jiang et al 2016;Mazzucchelli et al 2017;Reed et al 2017;Matsuoka et al 2019;Wang et al 2019;Yang et al 2019), but individual discoveries have pushed out the extremes of mass (Wu et al 2015;Yang et al 2020), luminosity (Pons et al 2019;Medvedev et al 2020), and redshift (Mortlock et al 2011;Bañados et al 2018c;Wang et al 2021b) that must be accounted for by theoretical models. Grappling with this challenge requires not only measuring quasar accretion rates, but also identifying mechanisms being used to produce massive growth.…”