Program: GN-2019B-FT-103

We propose Gemini/GNIRS spectroscopy of a new very luminous quasar PSO J045+05 at z=6.9 with the goal of measuring its black hole mass and chemical abundance. PSO J045+05 was discovered by us using the multiband near- and mid-infrared photometry, and was confirmed to be a high-redshift source by detecting the CO(6-5) and CO(7-6) emission lines from the molecular gas surrounding this quasar. PSO J045+05 with its absolute magnitude of M1450=-27.1, is currently the second most luminous quasar known at z>6.5. The luminosity of PSO J045+05 implies a more massive supermassive black hole than typically in quasars at z>6.5. The GNIRS spectrum of PSO J045+05 will include the CIV and MgII emission lines redshifted to 1.2 and 2.2 microns which will be used by us to measure its black hole mass. These observations have implications for the formation of supermassive black holes and for their coevolution with galaxy bulges. The flux ratios of the metal lines of PSO J045+05 between 0.9 and 2.5 microns ( SiIV/CIV , CIII]/CIV , FeII/MgII ) will also provide valuable constraints on the metallicity enrichment and ionization state of the circumnuclear gas of luminous quasars at early epochs.