AI 中文总结
该研究通过JWST光谱分析135个6≤z≤10星系，发现氮增强是高红移星系普遍特征，由标准增丰过程产生，核心方法为光谱堆叠与多电离区建模。
AI 中文摘要
詹姆斯·韦布空间望远镜（JWST）已发现越来越多红移z>6的星系具有增强的N/O比值，这对标准化学增丰框架提出了挑战。我们通过对135个星系进行堆叠分析，检验该现象是否仅存在于极端系统中，还是6≤z≤10星系群体的普遍特征；这些星系均具有JWST/NIRSpec（近红外光谱仪）R~1000分辨率的光谱，我们探测了氮（N）、碳（C）和氧（O）增丰的起源及其与近期恒星形成的依赖关系。全样本合成谱显示出显著的C III]、C IV、N IV]和He II发射线，证明高电离紫外线的普遍性。极光[O III]λ4363电子温度与多电离区建模给出直接-T_e丰度：在12+log(O/H)=7.79±0.03时，N/O的对数为-0.57±0.09，C/O的对数为-0.80±0.03；这与本地样本形成对比，表明在最初的10亿年内存在显著的氮增强。我们还按近期恒星形成活动（爆发时标Δt=3-20百万年）进行堆叠分析，发现处于近期爆发阶段的源，其N/O和金属丰度均低于相对平静阶段的源，最大差异出现在最短时标上；而C/O在所有指标中基本保持不变。我们将这些观测结果解释为多次爆发事件中渐近巨星支（AGB）增丰的延迟效应，以及原始气体流入的稀释作用共同导致。宇宙学模拟仅用核心坍缩超新星（CCSNe）和AGB的产额就能复现该趋势，无需更短寿命的（超）大质量恒星。因此，增强的N/O比值似乎是高红移星系的普遍特征，由标准增丰过程产生，无需新的物理框架。
英文摘要
The James Webb Space Telescope (JWST) has revealed a growing number of $z>6$ galaxies with enhanced N/O ratios that challenge standard chemical enrichment frameworks. We test whether this is exclusive to extreme systems or a generic feature of $6 \leq z \leq 10$ populations through a stacking analysis of 135 galaxies with JWST/NIRSpec $R\sim1000$ spectroscopy, probing the origin of N, C and O enrichment and its dependence on recent star formation. A full-sample composite reveals prominent C III], C IV, N IV] and He II emission, demonstrating a ubiquity of high-ionisation UV lines. Auroral [O III]$λ$4363 electron temperatures and multi-ionisation zone modelling yield direct-$T_e$ abundances with supersolar $\log(\mathrm{N/O}) = -0.57^{+0.09}_{-0.10}$ and subsolar $\log(\mathrm{C/O}) = -0.80^{+0.03}_{-0.03}$ at $12 + \log(\mathrm{O/H}) = 7.79^{+0.03}_{-0.03}$, in contrast with local samples and suggesting significant nitrogen enhancement within the first billion years. Stacking further by recent star formation activity over burst timescales of $Δt = 3$--$20$~Myr, we find that sources caught in a recent burst are less enriched in both N/O and metallicity than those in a relative lull, with the largest contrasts confined to the shortest timescales. C/O, however, remains largely invariant across all metrics. We interpret these observations as the result of delayed AGB enrichment across multiple burst episodes, together with dilution by pristine gas inflows. Cosmological simulations reproduce this trend with CCSNe and AGB yields alone, without the need for shorter-lived (super-)massive stars. Enhanced N/O therefore appears to be a generic feature of high-redshift systems, produced by standard enrichment processes rather than requiring new physical frameworks.
Comments20 pages, 7 figures, 6 tables. Submitted to MNRAS, comments welcome
