AI 中文总结
利用JWST/NIRSpec光谱，通过栅栏模型拟合星系光谱，不分解电离光子产生效率和逃逸率，得出电离输出，结合紫外光度函数推导5<z<15的电离光子预算，发现少数强泄漏星系驱动大部分再电离。
AI 中文摘要
宇宙最后一次主要相变——再电离时代（EoR）的成因仍然非常难以捉摸。虽然詹姆斯·韦布空间望远镜（JWST）已开始揭示早期星系的性质，但由于红移z>6时存在中性星系际介质（IGM），直接探测其电离光子几乎不可能，因此无法直接估计电离光子的逃逸率（fesc）。不过，逃逸率编码在对电离光子低不透明度的光谱特征中，即随着fesc增加，星云发射减少。本文利用DAWN JWST存档中红移5<z<10的大量JWST/NIRSpec光谱，对EoR星系的电离发射率和再电离时间线提供新的限制。通过用用于电离光子逃逸的栅栏模型对1428个星系进行详细光谱拟合，得出fesc的后验值以及有效电离输出。这种方法在不将其分解为电离光子产生效率和fesc的情况下，得出每个星系的逃逸电离输出。将这些测量结果与紫外光度函数（LFs）相结合，得出氢离子化LFs，从而得到5<z<15、积分至MUV=-13的观测推导电离光子预算。在标准假设下，我们的预算得出的IGM中性分数演化与独立探测结果一致，再电离在z~5.8结束。鉴于电离LF的演化形状，亮源（MUV~-20）在较低红移（z=5-6）时主导宇宙电离发射率nion，而在z>6时，暗星系（MUV>-18）贡献大致相同。值得注意的是，仅约20%的源（fesc>10%）产生了约87%的电离光子。总体而言，我们的结果支持少数强泄漏星系驱动大部分再电离的图景。
英文摘要
The sources responsible for the Epoch of Reionization (EoR), the last major phase transition of the Universe, remain highly elusive. While JWST has begun to illuminate the properties of early galaxies, the direct detection of their ionizing photons is virtually impossible due to the neutral intergalactic medium (IGM) at z>6. A direct estimate of the escape fraction of ionizing photons (fesc) is thus not possible. However, the escape fraction is encoded in spectral features that trace a low opacity to ionizing photons, namely the reduction of nebular emission with increasing fesc. Here, we exploit the large archive of JWST/NIRSpec spectra at 5<z<10 from the DAWN JWST Archive to provide new constraints on the ionizing emissivity of EoR galaxies and on the timeline of reionization. Through detailed spectral fitting of 1428 galaxies with a picket-fence model for the escape of ionizing photons, we derive posteriors of fesc together with the effective ionizing output. This approach yields the escaping ionizing output of each galaxy while bypassing the usual decomposition into the ionizing photon production efficiency and fesc. Combining these measurements with UV luminosity functions (LFs), we derive the hydrogen ionizing LFs, resulting in an observationally-derived ionizing photon budget at 5<z<15, integrated down to MUV=-13. Under standard assumptions, our budget yields an evolution of the IGM neutral fraction consistent with independent probes, with reionization ending at z~5.8. Given the evolving shape of the ionizing LF, bright sources (MUV ~ -20) dominate the cosmic ionizing emissivity nion at lower redshift (z=5-6), whereas at z>6 faint galaxies (MUV > -18) contribute roughly equally. Remarkably, a mere ~20% of sources, those with fesc>10%, produce ~87% of the ionizing photons. Overall, our results support a picture in which a few strongly leaking galaxies drive most of reionization.
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