Quantifying the Escape of Lyα at z ≈ 5–6: A Census of Lyα Escape Fraction with Hα-emitting Galaxies Spectroscopically Confirmed by JWST and VLT/MUSE

The Astrophysical Journal Supplement Series Pub Date : 2024-05-26 DOI:10.3847/1538-4365/ad3e7d

Xiaojing Lin, Zheng Cai, Yunjing Wu, Zihao Li, Fengwu Sun, Xiaohui Fan, Zuyi Chen, Mingyu Li, Fuyan Bian, Yuanhang Ning, Linhua Jiang, Gustavo Bruzual, Stephane Charlot and Jacopo Chevallard

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Abstract

The James Webb Space Telescope provides an unprecedented opportunity for unbiased surveys of Hα-emitting galaxies at z > 4 with the NIRCam's wide-field slitless spectroscopy (WFSS). In this work, we present a census of Lyα escape fraction (fesc,Lyα) of 165 star-forming galaxies at z = 4.9–6.3, utilizing their Hα emission directly measured from FRESCO NIRCam/WFSS data. We search for Lyα emission of each Hα-emitting galaxy in the Very Large Telescope/MUSE data. The overall fesc,Lyα measured by stacking is 0.090 ± 0.006. We find that fesc,Lyα displays a strong dependence on the observed UV slope (βobs) and E(B − V), such that the bluest galaxies (βobs ∼ −2.5) have the largest escape fractions (fesc,Lyα ≈ 0.6), indicative of the crucial role of dust and gas in modulating the escape of Lyα photons. fesc,Lyα is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in fesc,Lyα with them can be explained by their underlying coupling with E(B − V) or βobs. Our results suggest a tentative decline in fesc,Lyα at z ≳ 5, implying increasing intergalactic medium attenuation toward higher redshift. Furthermore, the dependence of fesc,Lyα on βobs is proportional to that of the ionizing photon escape fraction (fesc,LyC), indicating that the escape of Lyα and ionizing photon may be regulated by similar physical processes. With fesc,Lyα as a proxy to fesc,LyC, we infer that UV-faint (MUV > −16) galaxies contribute >70% of the total ionizing emissivity at z = 5–6. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe.

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量化z ≈ 5-6处的Lyα逃逸：由JWST和VLT/MUSE光谱仪确认的Hα发射星系的Lyα逃逸率普查

詹姆斯-韦伯太空望远镜（James Webb Space Telescope）为利用 NIRCam 的宽视场无缝光谱（WFSS）对 z > 4 的 Hα 发射星系进行无偏勘测提供了前所未有的机会。在这项工作中，我们利用 FRESCO NIRCam/WFSS 数据直接测量到的 165 个恒星形成星系的 Hα 发射，对 z = 4.9-6.3 的 Lyα 逃逸率（esc,Lyα）进行了普查。我们在甚大望远镜/MUSE数据中搜索每个Hα发射星系的Lyα发射。通过叠加测得的总体 fesc,Lyα 为 0.090 ± 0.006。我们发现，esc,Lyα与观测到的紫外斜率（βobs）和E(B - V)有很大的关系，因此最蓝的星系（βobs ∼ -2.5）具有最大的逃逸率（esc,Lyα ≈ 0.6），这表明尘埃和气体在调节Lyα光子逃逸方面起着至关重要的作用。fesc,Lyα与其他参数（包括紫外光度和恒星质量）的关系不那么密切，fesc,Lyα与它们的变化可以用它们与E（B - V）或βobs的潜在耦合来解释。我们的结果表明，在 z ≳ 5 时，fesc,Lyα 出现了暂时性的下降，这意味着星系间介质衰减在向更高红移方向增加。此外，fesc,Lyα对βobs的依赖性与电离光子逸出率（fesc,LyC）成正比，表明Lyα和电离光子的逸出可能受类似物理过程的调节。用 fesc,Lyα 代替 fesc,LyC，我们可以推断出，在 z = 5-6 时，UV-faint（MUV > -16）星系贡献了总电离发射率的 >70%。如果这些关系在再电离时期保持不变，那么紫外隐色星系就可以为宇宙的再电离贡献大部分紫外光子预算。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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