Probing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z ≤ 7.64
Journal
Date Issued
2021
Author(s)
Yang, Jinyi
•
Wang, Feige
•
Fan, Xiaohui
•
Barth, Aaron J.
•
Hennawi, Joseph F.
•
•
Bian, Fuyan
•
Davies, Frederick B.
•
Farina, Emanuele P.
•
Schindler, Jan Torge
•
Bañados, Eduardo
•
•
Eilers, Anna Christina
•
Green, Richard
•
Guo, Hengxiao
•
Jiang, Linhua
•
Li, Jiang Tao
•
Venemans, Bram
•
Walter, Fabian
•
Wu, Xue Bing
•
Yue, Minghao
Abstract
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) × 109 M ⊙, which requires massive seed black holes with masses ≳103–104 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.
Volume
923
Issue
2
Start page
262
Issn Identifier
0004-637X
Rights
open.access
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