Program: GN-2018A-C-1

Quasars at the epoch of reionization (EoR) provide direct probes of the evolution of supermassive black holes (SMBHs), the cosmic reionization history, and the build-up of most massive galaxies at cosmic dawn. Although more than 100 quasars have been discovered at z>6, only two quasars have been reported at z>7, and a handful at z>6.5, because of a combination of their declining spatial density and limited sky coverage of near infrared (NIR) photometry. Recently, we discovered six luminous quasars at z>6.5 based on newly available near-IR imaging surveys. Here, we propose to use Gemini/GMOS-N to obtain deep optical spectroscopic observations of four z>6.5 quasars that we do not have yet good quality optical spectra and to use Gemini/GNIRS to obtain deep NIR spectroscopic observations of two z>6.5 quasars that we do not have yet good quality NIR spectra. Combined with our current available high quality spectra of other quasars, the Gemini observations will provide crucial measurements of BH masses, Eddington ratios and chemical abundances in the quasar broad line regions and will allow detailed modeling of quasar absorption spectra, including the profile of Gunn-Peterson damping wing, the size of proximity zone and joint analysis of Lyman-alpha and Lyman-beta flux probability distribution functions. The proposed program will provide new constraints on the intergalactic medium (IGM) neutral fraction and UV background within EoR. Broad MgII emission line will also provide accurate, unbiased systemic redshifts of the quasar systems, critical to plan spectroscopic follow-up observations in (sub)mm wavelength to study the earliest SMBH/galaxy co-evolution. In addition, the high quality Gemini spectra will also allow us to identify weak high redshift intervening metal absorbers to probe the IGM chemical enrichment from early galaxies at z>6.