Metallicity in Quasar Broad-line Regions at Redshift ∼6
Research output: Contribution to journal › Journal article › Research › peer-review
Documents
- Wang_2022_ApJ_925_121
Final published version, 5.27 MB, PDF document
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 language | English |
---|---|
Article number | 121 |
Journal | Astrophysical Journal |
Volume | 925 |
Issue number | 2 |
Number of pages | 14 |
ISSN | 0004-637X |
DOIs | |
Publication status | Published - 1 Feb 2022 |
ID: 307503822