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arXiv 2406.07618astro-ph.GA
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挑战LyC-Lyα关系：z~2.3处无LyC泄漏的强Lyα发射体

Challenging the LyC-Ly$α$ relation: strong Ly$α$ emitters without LyC leakage at z $\sim$ 2.3

Annalisa Citro, Claudia M. Scarlata, Kameswara B. Mantha, Liliya R. Williams, Marc Rafelski, Mitchell Revalski, Matthew J. Hayes, Alaina Henry, Michael J. Rutko… 展开作者

Annalisa Citro, Claudia M. Scarlata, Kameswara B. Mantha, Liliya R. Williams, Marc Rafelski, Mitchell Revalski, Matthew J. Hayes, Alaina Henry, Michael J. Rutkowski, Harry I. Teplitz, Andrea Grazian, Anahita Alavi

备注：
23 Pages, 11 Figures. Accepted for publication in ApJ
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AI总结：

本文通过研究z~2.3处七个强Lyα发射的引力透镜星系，发现其LyC逃逸分数低于13%，挑战了Lyα作为再电离时期LyC逃逸间接指标的有效性。

摘要：

LyC电离辐射的逃逸分数（$f_{lyc}$）对于理解再电离至关重要，但在$z \gtrsim 4$处难以测量。近期研究集中于在$z \sim 0.3$处校准$f_{lyc}$的间接指标，发现$Lyα$与其密切相关。目前仍不清楚的是，LyC $-$ $Lyα$关系是否随红移演化，以及$Lyα$在再电离时期是否真正适用作$f_{lyc}$指标。在本研究中，我们研究了来自BELLS GALLERY Survey的七个$-21 \lesssim M_{UV} \lesssim-19$的引力透镜星系，红移为$z\sim2.3$。我们的目标具有静止系$Lyα$等效宽度在40 Å至200 Å之间以及低尘埃含量（$-2.4 \lesssim β\lesssim -2.0$），这两者都指示高LyC逃逸。令人惊讶的是，使用哈勃太空望远镜F275W和F225W成像对$f_{lyc}$的直接估计表明，我们的目标不是LyC发射体，绝对$f_{lyc} < 13 \\%$（假设中值IGM透射率）。低$f_{lyc}$与高$Lyα$等效宽度和逃逸分数相结合，可能归因于中性氢柱密度和尘埃含量随红移的演化，以及高红移星系中光学厚气体的覆盖分数低于1。此外，我们的分析表明，每个透镜成分的发射被均匀吸收。我们的结果挑战了将基于$z\sim0$ $Lyα$的LyC间接估计量外推到再电离时期的有效性。

英文摘要：

The escape fraction of LyC ionizing radiation ($f_{lyc}$) is crucial for understanding reionization, yet difficult to measure at $z \gtrsim 4$. Recently, studies have focused on calibrating indirect indicators of $f_{lyc}$ at $z \sim 0.3$, finding that $Lyα$ is closely linked to it. What is still unclear is whether the LyC $-$ $Lyα$ relation evolves with redshift, and if $Lyα$ is truly applicable as an $f_{lyc}$ indicator during the reionization epoch. In this study, we investigate seven $-21 \lesssim M_{UV} \lesssim-19$ gravitationally lensed galaxies from the BELLS GALLERY Survey at $z\sim2.3$. Our targets have rest-frame $Lyα$ equivalent widths between 40 Å and 200 Å and low dust content ($-2.4 \lesssim β\lesssim -2.0$), both indicative of high LyC escape. Surprisingly, direct estimates of $f_{lyc}$ using Hubble Space Telescope imaging with F275W and F225W reveal that our targets are not LyC emitters, with an absolute $f_{lyc} < 13 \%$ (assuming the median IGM transmission). The low $f_{lyc}$, coupled with the high $Lyα$ equivalent width and escape fraction, could potentially be attributed to the redshift evolution of the neutral hydrogen column density and dust content, as well as covering fractions of optically thick gas below 1 in high redshift galaxies. Additionally, our analysis suggests that the emission for each lensed component is uniformly absorbed. Our results challenge the validity of the extrapolation of $z\sim0$ Ly$α$-based LyC indirect estimators into the reionization epoch.

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