Metallicity in Quasar Broad-line Regions at Redshift ∼6

Shu Wang, Linhua Jiang, Yue Shen, Luis C. Ho, Marianne Vestergaard, Eduardo Bañados, Chris J. Willott, Jin Wu, Siwei Zou, Jinyi Yang, Feige Wang, Xiaohui Fan, Xue Bing Wu

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Article number121
JournalAstrophysical Journal
Volume925
Issue number2
DOIs
StatePublished - Feb 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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