Search for Z~7 Quasars Using Alma Co Spectral Scans and Near-Infrared Spectroscopy(1/3)

High-redshift quasars are unique objects for studies of the early epochs of our Universe. Their optical/near-infrared spectra provide important constraints on the ionization state of the intergalactic medium at the epoch of reionization and on the masses of the first supermassive black holes formed in the Universe. The submillimeter observations of the host galaxies of high-redshift quasars help to understand how supermassive black holes and their host galaxies formed in the Universe. Recent big optical and near-infrared surveys and developments in instrumentation made it possible to observe quasars at redshifts 6.5<z<7.5, well before the end of the epoch of reionization. However, only two quasars have been found at z > 7. We proposed and tested a new method for the redshift survey of quasars at z>6.5 using submillimeter spectroscopy with ALMA. The method is based on the observations of the emission lines of carbon monoxide at high rotational transitions expected from the host galaxies of high-redshift quasars with active star formation. We successfully detected emission lines of carbon monoxide from about a dozen quasar candidates at redshifts 6.5<z<7.5 selected by us from the Pan-STARRs survey. Moreover, we have discovered three new quasars at z>7 and almost doubled the number of the quasars known at z>7. The spatial distribution of the carbon monoxide gas around the discovered quasars indicates that their host galaxies have close companion protogalaxies at different stages of interaction composed mostly of molecular gas. The discovery of these companion protogalaxies provides first direct evidence for enormous amounts of raw molecular gas surrounding supermassive black holes at early epochs. We also detected, for the first time, the emission lines of water vapour from some of the newly discovered quasars. The detected water emission suggests very high densities and temperatures in the star-forming regions of the galaxies in the young Universe which are not typically observed in galaxies at low redshifts. In the current project we propose detailed study of the high-redshift quasars discovered by us. Our study will include 1) measurements of the molecular gas mass; 2) estimation of the star-formation rates; 3) study of the nearest environment and 4) measurements of the black hole masses of newly discovered z>7 quasars. By studying these quasars, we, for the first time, will obtain valuable information on the very early stages of star formation in the galaxies hosting growing supermassive black holes at the early epochs of our Universe.