Abstract
Abstract We report the discovery of a luminous quasar, J1007+2115 at z = 7.515 (“Pōniuā‘ena”), from our wide-field reionization-era quasar survey. J1007+2115 is the second quasar now known at z > 7.5, deep into the reionization epoch. The quasar is powered by a (1.5 ± 0.2) × 109 M ⊙ supermassive black hole (SMBH), based on its broad Mg ii emission-line profile from Gemini and Keck near-IR spectroscopy. The SMBH in J1007+2115 is twice as massive as that in quasar J1342+0928 at z = 7.54, the current quasar redshift record holder. The existence of such a massive SMBH just 700 million years after the Big Bang significantly challenges models of the earliest SMBH growth. Model assumptions of Eddington-limited accretion and a radiative efficiency of 0.1 require a seed black hole of ≳104 M ⊙ at z = 30. This requirement suggests either a massive black hole seed as a result of direct collapse or earlier periods of rapid black hole growth with hyper-Eddington accretion and/or a low radiative efficiency. We measure the damping wing signature imprinted by neutral hydrogen absorption in the intergalactic medium (IGM) on J1007+2115's Lyα line profile, and find that it is weaker than that of J1342+0928 and two other z ≳ 7 quasars. We estimate an IGM volume-averaged neutral fraction . This range of values suggests a patchy reionization history toward different IGM sightlines. We detect the 158 μm [C ii] emission line in J1007+2115 with the Atacama Large Millimeter/submillimeter Array; this line centroid yields a systemic redshift of z = 7.5149 ± 0.0004 and indicates a star formation rate of ∼210 M ☉ yr−1 in its host galaxy.
Highlights
Luminous reionization-era quasars (z > 6.5) provide unique probes of supermassive black hole (SMBH) growth, massive galaxy formation, and intergalactic medium (IGM) evolution in the first billion years of the Universe’s history
We detect the 158 μm [C II] emission line in J1007+2115 with ALMA; this line centroid yields a systemic redshift of z = 7.5149 ± 0.0004 and indicates a star formation rate of ∼ 210 M yr−1 in its host galaxy
It is difficult to draw solid conclusions because of the large uncertainties on the value of xHI, the much weaker damping wing seen in J1007+2115’s spectrum indicates a significant scatter of the IGM neutral fraction in the redshift range z = 7.5 to z = 7.0, which can be interpreted as observational evidence of patchy reionization
Summary
Luminous reionization-era quasars (z > 6.5) provide unique probes of supermassive black hole (SMBH) growth, massive galaxy formation, and intergalactic medium (IGM) evolution in the first billion years of the Universe’s history. During the past few years, high-redshift quasar searches using newly available wide-area optical and IR surveys have resulted in a sixfold increase in the number of known quasars at z > 6.5: 47 luminous quasars at z > 6.5 have been discovered (e.g., Fan et al 2019; Venemans et al 2013, 2015; Wang et al 2019; Mazzucchelli et al 2017; Reed et al 2019; Matsuoka et al 2019a; Yang et al 2019), among them only six are at z ≥ 7 (Mortlock et al 2011; Wang et al 2018; Matsuoka et al 2019a,b; Yang et al 2019) and one at z > 7.1 (Banados et al 2018) These discoveries show that 800 million solar-mass black holes exist already at z = 7.5 (Banados et al 2018) and that the IGM is significantly neutral at z 7 Photometric data are reported on the AB system after applying a Galactic extinction correction (Schlegel et al 1998; Schlafly & Finkbeiner 2011)
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