%AYang, Jinyi%AWang, Feige%AFan, Xiaohui%ABarth, Aaron%AHennawi, Joseph%ANanni, Riccardo%ABian, Fuyan%ADavies, Frederick%AFarina, Emanuele%ASchindler, Jan-Torge%ABañados, Eduardo%ADecarli, Roberto%AEilers, Anna-Christina%AGreen, Richard%AGuo, Hengxiao%AJiang, Linhua%ALi, Jiang-Tao%AVenemans, Bram%AWalter, Fabian%AWu, Xue-Bing%AYue, Minghao%BJournal Name: The Astrophysical Journal; Journal Volume: 923; Journal Issue: 2 %D2021%I %JJournal Name: The Astrophysical Journal; Journal Volume: 923; Journal Issue: 2 %K %MOSTI ID: 10324264 %PMedium: X %TProbing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z ≤ 7.64 %XAbstract We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 < z ≤ 7.64, including 32 quasars at z > 6.5, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the Mg ii emission lines are in the range (0.3–3.6) × 10 9 M ⊙ , which requires massive seed black holes with masses ≳10 3 –10 4 M ⊙ , assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv –Mg ii emission-line velocity differences in our sample show an increase of C iv 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 Fe ii /Mg ii 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 C iv 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. %0Journal Article