IGM/CGM 富集对宇宙最初6亿年化学丰度确定的重要性
On the importance of the IGM/CGM enrichment in determining chemical abundances during the first 600 Myr
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中文总结 AI 辅助
本研究开发纳入IGM/CGM多源富集与高红移星系观测SFHs的化学演化模型，发现IGM/CGM化学组成对z>8星系丰度比的关键作用，且SMSs是早期丰度的重要来源。
中文摘要 AI 辅助
詹姆斯·韦布空间望远镜（JWST）观测显示，红移z>8的星系在固定金属丰度下呈现出大范围的碳氧比（C/O），且氮氧比（N/O）相比本地星系系统性升高。已提出的解释包括精细调节的恒星形成历史（SFHs）、差速或原始气体流入、顶端或底端偏重的初始质量函数，以及来自沃尔夫-拉叶星、超大质量恒星（SMSs）或第三星族星的富集。观测到的丰度既反映了与SFHs相关的原位产生，也反映了为恒星形成提供燃料的气体流入源——星系际介质与星系周介质（IGM/CGM）的早期预富集。在如此早期的时代，SFHs必然短暂，持续的恒星形成需要流入量超过流出量，这使得IGM/CGM的化学状态尤为重要。我们开发了一个化学演化模型，该模型纳入了（1）多种源对IGM/CGM的富集，以及（2）高红移星系的观测SFHs。将该模型应用于8个z>8的星系，我们发现只有特定的预富集场景能重现其观测到的丰度比。例如，GN-z11和CEERS-1019中测得的低C/O和高N/O比，要求IGM/CGM被SMSs富集且预富集至氧金属丰度约为太阳值的10^-5。我们还发现，log(N/O)与12+log(O/H)平面比log(C/O)与12+log(O/H)平面对富集路径提供了更严格的约束。总体而言，我们的结果强调了IGM/CGM化学组成在z>8化学演化模型中的关键作用，并凸显了SMSs对早期碳、氮、氧丰度的显著影响。
英文摘要
JWST observations show that galaxies at $z>8$ exhibit a wide range of carbon-to-oxygen (C/O) ratios at fixed metallicity and systematically elevated nitrogen-to-oxygen (N/O) ratios compared to local galaxies. Proposed explanations include finely tuned star-formation histories (SFHs), differential or pristine inflows, top- or bottom-heavy initial mass functions, or enrichment from Wolf-Rayet stars, supermassive stars (SMSs), or Population III stars. The observed abundances reflect both in situ production tied to the SFHs and earlier pre-enrichment of the intergalactic and circumgalactic medium (IGM/CGM), which supply the gas inflow that fuels star formation. At such early epochs, SFHs are necessarily brief, and sustained star formation requires inflows to dominate over outflows, making the chemical state of the IGM/CGM especially important. We develop a chemical evolution model that incorporates (1) enrichment of the IGM/CGM by multiple sources and (2) the observed SFHs of high-redshift galaxies. Applying this model to eight galaxies at $z>8$, we find that only specific pre-enrichment scenarios reproduce their observed abundance ratios. For example, the low C/O and high N/O ratios measured in GN-z11 and CEERS-1019 require an IGM/CGM enriched by SMSs and pre-enriched to an oxygen metallicity of $\sim10^{-5}$ of the solar value. We also find that the log(N/O) vs. 12 + log(O/H) plane provides more stringent constraints on enrichment pathways than the log(C/O) vs. 12 + log(O/H) plane. Overall, our results highlight the crucial role of IGM/CGM chemical composition in chemical evolution models at $z>8$ and underscore the significant influence of SMSs on early carbon, nitrogen, and oxygen abundances.
