@article{8701222ef3fc439f942ba4b3a5d7cb94,
title = "Metallicity in Quasar Broad-line Regions at Redshift ∼6",
abstract = "Broad-line regions (BLRs) in high-redshift quasars provide crucial information on chemical enrichment in the early universe. Here we present a study of BLR metallicities in 33 quasars at redshift 5.7 < z < 6.4. Using the near-IR spectra of the quasars obtained from the Gemini telescope, we measure their rest-frame UV emission-line flux and calculate flux ratios. We then estimate BLR metallicities with empirical calibrations based on photoionization models. The inferred median metallicity of our sample is a few times the solar value, indicating that the BLR gas had been highly metal enriched at z ∼6. We compare our sample with a low-redshift quasar sample with similar luminosities and find no evidence of redshift evolution in quasar BLR metallicities. This is consistent with previous studies. The Fe ii/Mg ii flux ratio, a proxy for the Fe/α element abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation at z ∼6. We also find that the black hole mass-BLR metallicity relation at z ∼6 is consistent with the relation measured at 2 < z < 5, suggesting that our results are not biased by a selection effect due to this relation.",
author = "Shu Wang and Linhua Jiang and Yue Shen and Ho, {Luis C.} and Marianne Vestergaard and Eduardo Ba{\~n}ados and Willott, {Chris J.} and Jin Wu and Siwei Zou and Jinyi Yang and Feige Wang and Xiaohui Fan and Wu, {Xue Bing}",
note = "Funding Information: We are grateful to the anonymous referee for the useful comments. We thank Hiroaki Sameshima for providing their measurements and Ping Chen, Fei Xu, and Hengxiao Guo for useful discussion. S.W., L.J., L.H., J.W., Z.S., and X.W. acknowledge support from the National Key R&D Program of China (grant Nos. 2016YFA0400703, 2016YFA0400702) and the National Science Foundation of China (grant Nos. 11721303, 11890693, 11991052). Y.S. acknowledges support from NSF grant Nos. AST-1715579 and AST-2009947. M.V. gratefully acknowledges financial support from the Independent Research Fund Denmark via grant number DFF 8021-00130. F.W. acknowledges the support by NASA through the NASA Hubble Fellowship grant #HST-HF2-51448.001-A and #HF2-51434 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Publisher Copyright: {\textcopyright} 2022. The Author(s). Published by the American Astronomical Society.",
year = "2022",
month = feb,
day = "1",
doi = "10.3847/1538-4357/ac3a69",
language = "English",
volume = "925",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "Institute of Physics Publishing, Inc",
number = "2",
}