Metallicity in Quasar Broad-line Regions at Redshift ∼ 6
Metallicity in Quasar Broad-line Regions at Redshift ∼ 6
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DOI：
10.3847/1538-4357/ac3a69
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发表时间：
2021-12
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通讯作者：
Shu I. Wang;Linhua Jiang;Yue Shen;L. Ho;M. Vestergaard;E. Bañados;C. Willott;Jin Wu;S. Zou;Jinyi Yang;Feige Wang;Xiaohui Fan;Xue-bing Wu
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作者：
Shu I. Wang;Linhua Jiang;Yue Shen;L. Ho;M. Vestergaard;E. Bañados;C. Willott;Jin Wu;S. Zou;Jinyi Yang;Feige Wang;Xiaohui Fan;Xue-bing Wu
高红移类星体中的宽线区（BLR）提供了有关早期宇宙化学富集的关键信息。本文对33个红移5.7 < z < 6.4的类星体的BLR金属丰度进行了研究。利用Gemini望远镜获得的类星体的近红外光谱，我们测量了它们的静止坐标系紫外发射线通量并计算了通量比。然后，我们估计BLR金属丰度与经验校准的基础上光电离模型。我们的样品的推断中值金属丰度是太阳值的几倍，表明BLR气体在z = 6时高度富集金属。我们比较我们的样品与一个低红移的类星体样品具有相似的光度，并没有发现证据红移演化类星体BLR金属丰度。这与以前的研究是一致的。Fe ii/Mg ii的通量比（代表Fe/α元素丰度比）也没有显示红移演化，进一步支持了在z = 6时快速形成核星星。我们还发现，黑洞质量-BLR金属丰度关系在z = 6时与在2 < z < 5时测量的关系是一致的，这表明我们的结果不会由于这种关系而受到选择效应的影响。
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.