We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3=10^3^-10^4^M_{sun}, assuming Eddington accretion since z=30. The Eddington ratio distribution peaks at {lambda}_Edd~0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The CIV-MgII emission-line velocity differences in our sample show an increase of CIV blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The FeII/MgII flux ratios derived for these quasars up to z=7.6, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for z>6.5 quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the CIV line. Our sample yields a strong broad absorption line quasar fraction of ~24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects.

Cone search capability for table J/ApJ/923/262/table1 (Quasar and observation information of the 37 quasars in the sample)

Cone search capability for table J/ApJ/923/262/table2 (Spectral fitting and quasar properties)

Cone search capability for table J/ApJ/923/262/table4 (Quasar BH masses derived from the spectral fitting based on the Vestergaard & Wilkes (2001ApJS..134....1V ; VW01) iron template)