Gemini GNIRS near-infrared spectroscopy of 50 quasars at z>~5.7
  We report initial results from a large Gemini program to observe z>~5.7
quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with
simultaneous ~0.85-2.5 micron spectra covering the rest-frame ultraviolet and
major broad emission lines from Ly-alpha to MgII. We present spectral
measurements for these quasars and compare to 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>~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 ~0.3. There is no evidence for super-Eddington accretion or
hypermassive (>10^10 Msun) black holes within our sample. We find a mild excess
of quasars with weak CIV 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.
