Discovery of Super-enriched Gas ∼1 Gyr after the Big Bang
Discovery of Super-enriched Gas ∼1 Gyr after the Big Bang
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DOI：
10.3847/2041-8213/aceefe
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发表时间：
2023-08
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通讯作者：
Jianghao 江豪 Huyan 呼延;V. Kulkarni;Suraj Poudel;N. Tejos;C. Péroux;S. López
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作者：
Jianghao 江豪 Huyan 呼延;V. Kulkarni;Suraj Poudel;N. Tejos;C. Péroux;S. López
高红移星系的星际和环星系介质中化学元素的丰度对早期恒星的核合成提供了重要的限制。高红移背景类星体光谱中的阻尼Lyα吸收体（DLAs）是获得遥远星系元素丰度可靠测量的理想场所。过去对红移z > 4的DLAs的研究测量到的丰度为0.01太阳。在这里，我们报告发现的DLA在z = 4.7372具有非常高的化学富集度。我们估计该吸收体中的H i柱密度为log（N H I/cm−2）= 20.48 ± 0.15。我们的分析显示碳和氧的丰度异常高（[C/H] = 0.88 ± 0.17，[O/H] = 0.71 ± 0.16）。如此高的浓缩水平在大爆炸后仅仅1.2 Gyr是令人惊讶的，因为没有足够的时间形成所需的星星。据我们所知，这是在z > 4.5时发现的第一个超太阳吸收体。我们发现Si和Mg的丰度为[Si/H] = −0.56−0.35+0.40和[Mg/H] = 0.59−0.50+0.27，证实了这种吸收体的富金属性质。相比之下，Fe的丰度要低得多（[Fe/H] = −1.53−0.15+0.15）。我们讨论了我们的研究结果对银河系化学演化模型的影响。该吸收剂的金属丰度高于任何其他已知的DLA的金属丰度，并且比化学演化模型的预测和来自先前研究的在z > 4.5处的NHI加权平均金属丰度高>2个数量级。相对丰度（例如，[O/Fe] = 2.29 ± 0.05，[C/Fe] = 2.46 ± 0.08）与早期恒星的富集预测相比也非常不寻常。
Abundances of chemical elements in the interstellar and circumgalactic media of high-redshift galaxies offer important constraints on the nucleosynthesis by early generations of stars. Damped Lyα absorbers (DLAs) in spectra of high-redshift background quasars are excellent sites for obtaining robust measurements of element abundances in distant galaxies. Past studies of DLAs at redshifts z > 4 have measured abundances of ≲0.01 solar. Here we report the discovery of a DLA at z = 4.7372 with an exceptionally high degree of chemical enrichment. We estimate the H i column density in this absorber to be log (N H I/cm−2) = 20.48 ± 0.15. Our analysis shows unusually high abundances of carbon and oxygen ([C/H] = 0.88 ± 0.17, [O/H] = 0.71 ± 0.16). Such a high level of enrichment a mere 1.2 Gyr after the Big Bang is surprising because of insufficient time for the required amount of star formation. To our knowledge, this is the first supersolar absorber found at z > 4.5. We find the abundances of Si and Mg to be [Si/H] = −0.56−0.35+0.40 and [Mg/H] = 0.59−0.50+0.27 , confirming the metal-rich nature of this absorber. By contrast, Fe shows a much lower abundance ([Fe/H] = −1.53−0.15+0.15 ). We discuss implications of our results for galactic chemical evolution models. The metallicity of this absorber is higher than that of any other known DLA and is >2 orders of magnitude above predictions of chemical evolution models and the N H I-weighted mean metallicity from previous studies at z > 4.5. The relative abundances (e.g., [O/Fe] = 2.29 ± 0.05, [C/Fe] = 2.46 ± 0.08) are also highly unusual compared to predictions for enrichment by early stars.