Yang, JinyiJinyiYangWang, FeigeFeigeWangFan, XiaohuiXiaohuiFanHennawi, Joseph F.Joseph F.HennawiDavies, Frederick B.Frederick B.DaviesYue, MinghaoMinghaoYueBanados, EduardoEduardoBanadosWu, Xue-BingXue-BingWuVenemans, BramBramVenemansBarth, Aaron J.Aaron J.BarthBian, FuyanFuyanBianBoutsia, KonstantinaKonstantinaBoutsiaDECARLI, ROBERTOROBERTODECARLIFarina, Emanuele PaoloEmanuele PaoloFarinaGreen, RichardRichardGreenJiang, LinhuaLinhuaJiangLi, Jiang-TaoJiang-TaoLiMazzucchelli, ChiaraChiaraMazzucchelliWalter, FabianFabianWalter2021-12-282021-12-2820202041-8205http://hdl.handle.net/20.500.12386/31266We 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) × 10<SUP>9</SUP> M<SUB>⊙</SUB> 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 ≳10<SUP>4</SUP> M<SUB>⊙</SUB> 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 $\langle {X}_{{\rm{H}}{\rm{I}}}\rangle ={0.39}_{-0.13}^{+0.22}$ . 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<SUB>⊙</SUB> yr<SUP>-1</SUP> in its host galaxy.STAMPAenArticle10.3847/2041-8213/ab9c262-s2.0-85091393708WOS:000548369300001https://iopscience.iop.org/article/10.3847/2041-8213/ab9c26https://api.elsevier.com/content/abstract/scopus_id/850913937082020ApJ...897L..14YFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation