AffiliationSteward Observatory, University of Arizona
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PublisherIOP Publishing Ltd
CitationWang, S., Jiang, L., Shen, Y., Ho, L. C., Vestergaard, M., Bañados, E., Willott, C. J., Wu, J., Zou, S., Yang, J., Wang, F., Fan, X., & Wu, X.-B. (2022). Metallicity in Quasar Broad-line Regions at Redshift ∼6. Astrophysical Journal.
RightsCopyright © 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.
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AbstractBroad-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. © 2022. The Author(s). Published by the American Astronomical Society.
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Except where otherwise noted, this item's license is described as Copyright © 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.