詹姆斯·韦布空间望远镜（JWST）致密宽线发射体的电离特性
The ionizing properties of JWST's compact broad-line emitters
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中文总结 AI 辅助
本研究基于JWST发现的z>4的宽线发射体，通过DJA普查4≤z≤7的致密蓝色宽线发射体样本，发现其电离特性及逃逸分数特征，表明宽线源在数Mpc尺度上可主导再电离贡献。
中文摘要 AI 辅助
近期詹姆斯·韦布空间望远镜（JWST）在红移z>4处发现了大量宽线发射体（BLEs），这重新引发了一个问题：除了暗弱星系之外的源是否对宇宙再电离有显著贡献。为评估这一贡献，我们对从DJA中选出的4≤z≤7范围内的致密蓝色宽线发射体进行了系统普查，旨在分离出紫外连续谱与宽线发射源自同一致密物理区域的源。我们从包含4145个拥有NIRSpec/PRISM光谱和NIRCam成像的星系的母样本出发，对宽氢α发射线（半高全宽FWHM>2000km s-1，信噪比S/N≥5，在宽氢α光度L_Ha,broad≥10^42.7erg s-1处完整）、蓝色连续谱斜率（紫外β_UV≤-1.5，光学β_opt<0.5）以及静止帧紫外和光学波段的形态致密性应用筛选标准，最终得到20个源的样本，占PRISM选出的宽线样本的约20%，该样本以小红点（LRDs）为主。我们发现，致密蓝色宽线发射体与恒星形成星系和小红点相比，呈现出高温电离连续谱、高电离紫外线（碳IV、氮IV]、氦II）以及升高的莱曼α发射体占比（X_Lya=50-67%）。除了同样缺乏X射线发射外，它们的光学光谱与小红点非常相似，这表明致密蓝色宽线发射体将该群体延伸到了更低的柱密度包层，但具有相似的能源，而非代表物理上不同的群体。使用Sirocco建模重现观测光谱的物理构型，我们发现最蓝的源具有高电离光子产生效率（logξ_ion~25.4Hz erg-1），加权平均逃逸分数fesc~0.2，而小红点的fesc~0.01。这意味着宽线源在全球范围内并不主导再电离，但考虑到它们的光度，其贡献可在数个百万秒差距（Mpc）尺度上占主导。
英文摘要
The recent JWST discovery of a numerous population of broad-line emitters (BLEs) at $z>4$ has reopened the question of whether sources other than faint galaxies contributed significantly to cosmic reionization. To assess this contribution, we present a systematic census of compact, blue broad-line emitters at $4\leq z\leq7$ selected from the DJA, designed to isolate sources in which the UV continuum and the broad-line emission originate from the same compact physical region. Starting from a parent sample of 4145 galaxies with NIRSpec/PRISM spectroscopy and NIRCam imaging, we apply criteria on broad Ha emission (FWHM$>2000$km s-1, detected at S/N$\geq5$, complete at $L_{Ha,broad}\geq10^{42.7}$erg s-1), blue continuum slopes ($β_{UV}\leq-1.5$, $β_{opt}<0.5$), and morphological compactness in both the rest-frame UV and optical, returning a final sample of 20 sources. This constitutes $\sim20%$ of the PRISM-selected broad-line sample, which is dominated by Little Red Dots (LRDs). We find that the compact blue BLEs display hot ionizing continua, high-ionization UV lines (CIV, NIV], HeII), and elevated Lya emitter fractions ($X_{Lya}=50-67%$) relative to star-forming galaxies and LRDs. Beyond their similar lack of X-ray emission, their optical spectra closely resemble those of LRDs. This suggests that compact blue BLEs extend this population towards lower column density envelopes, but with similar engines, rather than representing a physically distinct population. Using Sirocco to model physical configurations that reproduce the observed spectra, we find a high ionizing photon production efficiency (log$ξ_{ion}\sim25.4$Hz erg-1) and a weighted average escape fraction $fesc\sim0.2$ for the bluest sources, and $\sim0.01$ for LRDs. This implies that broad-line sources do not dominate reionization globally, but given their luminosity, their contribution can dominate up to few Mpc scales.
