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Title: Metallicity in Quasar Broad-line Regions at Redshift ∼ 6

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 atz∼ 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 Feii/Mgiiflux ratio, a proxy for the Fe/αelement abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation atz∼ 6. We also find that the black hole mass–BLR metallicity relation atz∼ 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.

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Award ID(s):
2009947 1908284
Publication Date:
Journal Name:
The Astrophysical Journal
Page Range or eLocation-ID:
Article No. 121
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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