Gemini GNIRS Near-infrared Spectroscopy of 50 Quasars at z ≳ 5.7

We report initial results from a large Gemini program to observe z greater than or similar to 5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with simultaneous similar to 0.85-2.5 mu m spectra covering the rest-frame ultraviolet and major broad emission lines from Ly alpha to Mg II. We present spectral measurements for these quasars and compare with their lower redshift counterparts at z = 1.5-2.3. We find that when quasar luminosity is matched, there are no significant differences between the rest-UV spectra of z greater than or similar to 5.7 quasars and the low-z comparison sample. High-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average Eddington ratio of similar to 0.3. There is no evidence for super-Eddington accretion or hypermassive (> 10(10) M-circle dot) black holes within our sample. We find a mild excess of quasars with weak C IV lines relative to the control sample. Our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts.