Discovery of the First Low-luminosity Quasar at z > 7

Abstract

We report the discovery of a quasar at z = 7.07, which was selected from the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. This quasar, HSC J124353.93+010038.5, has an order of magnitude lower luminosity than do the other known quasars at z > 7. The rest-frame ultraviolet absolute magnitude is M 1450 = −24.13 ± 0.08 mag and the bolometric luminosity is erg s−1. Its spectrum in the optical to near-infrared shows strong emission lines, and shows evidence for a fast gas outflow, as the C iv line is blueshifted and there is indication of broad absorption lines. The Mg ii-based black hole mass is , thus indicating a moderate mass accretion rate with an Eddington ratio . It is the first z > 7 quasar with sub-Eddington accretion, besides being the third most distant quasar known to date. The luminosity and black hole mass are comparable to, or even lower than, those measured for the majority of low-z quasars discovered by the Sloan Digital Sky Survey, and thus this quasar likely represents a z > 7 counterpart to quasars commonly observed in the low-z universe.

New constraints on quasar evolution: broad-line velocity shifts over 1.5 ≲ z ≲ 7.5

“…Such a strategy is obviously very challeng-ing. However, the discovery of a faint z ∼ 7 quasar with a significant C IV blueshift (∼ 2500 km s −1 ) in the Subaru High-z Exploration of Low-Luminosity Quasars survey (SHELLQS) provides marginal evidence against this interpretation (Matsuoka et al 2019) while a recent small sample of six relatively faint quasars at z ∼ 6.3 show mixed results including potentially the first C IV redshift with respect to Mg II at z > 6 ( Onoue et al 2019). Clearly a larger sample of fainter, possibly lensed quasars above z 6 can test this hypothesis.…”

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). VI. Black Hole Mass Measurements of Six Quasars at 6.1 ≤ z ≤ 6.7

“…The Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP; Aihara et al 2018) has covered ∼ 400 deg 2 with five broad-band filters (grizy) to full depth (5σ depth z lim,5σ = 25.5 mag) between 2014 Spring and 2019 March, powered by the wide field-ofview of the HSC (1.5 degrees in diameter; Miyazaki et al 2018). With this survey, our team has recently discovered more than 80 low-luminosity quasars at z ∼ 6 − 7 (Matsuoka et al 2016(Matsuoka et al , 2018a(Matsuoka et al ,b, 2019, with the highestredshift one at z = 7.07 (HSC J1243+0100; Matsuoka et al 2019). The number of the HSC quasars is already comparable to other major surveys such as the Sloan Digital Sky Survey (SDSS; York et al 2000;Jiang et al 2016) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1, PS1; Kaiser et al 2010;Bañados et al 2016), but the luminosity range of the HSC quasars is about an order of magnitude fainter than those luminous quasars, extending down to M 1450 ∼ −22 mag.…”

“…On the other hand, it is remarkable that the other HSC quasars are powered by 10 9 M SMBHs with sub-Eddington accretion, as does HSC J1243+0100 (M BH = (3.3 ± 2.0) × 10 8 M , L bol /L Edd = 0.34 ± 0.20;Matsuoka et al 2019). The average Eddington ratio of those six sub-Eddington quasars (i.e., excluding J0859+0022) is L bol /L Edd = 0.24 ± 0.10.…”

The Birth of Binary Direct-collapse Black Holes

“…More than 300 quasars have now been discovered at z > 6 (e.g., Fan et al 2003), including seven at z > 7 ( Mortlock et al 2011;Bañados et al 2018;Matsuoka et al 2019). The formation of such massive black holes less than a Gyr after the Big Bang poses serious challenges for paradigms of early structure formation.…”