TY - JOUR
T1 - Metallicity in Quasar Broad-line Regions at Redshift ∼6
AU - Wang, Shu
AU - Jiang, Linhua
AU - Shen, Yue
AU - Ho, Luis C.
AU - Vestergaard, Marianne
AU - Bañados, Eduardo
AU - Willott, Chris J.
AU - Wu, Jin
AU - Zou, Siwei
AU - Yang, Jinyi
AU - Wang, Feige
AU - Fan, Xiaohui
AU - Wu, Xue Bing
N1 - Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/2/1
Y1 - 2022/2/1
N2 - 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.
AB - 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.
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U2 - 10.3847/1538-4357/ac3a69
DO - 10.3847/1538-4357/ac3a69
M3 - Article
AN - SCOPUS:85125859866
SN - 0004-637X
VL - 925
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 121
ER -