No missing photons for reionization: moderate ionizing photon escape fractions from the FIRE-2 simulations
No missing photons for reionization: moderate ionizing photon escape fractions from the FIRE-2 simulations
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DOI：
10.1093/mnras/staa2404
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发表时间：
2020-03
影响因子：
4.8
通讯作者：
Xiangcheng Ma;E. Quataert;A. Wetzel;P. Hopkins;C. Faucher-Giguère;D. Keres̆
中科院分区：
文献类型：
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作者：
Xiangcheng Ma;E. Quataert;A. Wetzel;P. Hopkins;C. Faucher-Giguère;D. Keres̆
我们给出了在现实环境反馈项目中对z≥5星系的34个高分辨率宇宙放大模拟的氢电离光子逃逸分数(FESC)，并用电离辐射蒙特卡罗辐射转移程序进行了后处理。在z=5-12时，我们的样本由8,500个晕组成，在M*∼108-$10^{12}，M_(Oot)$(M*∼104-$10^{10}，M_(Oot)$)。我们发现，在109.5-$10^{11}，M_(Oot)}$时，样本的平均值随着晕质量的增加而增加，并在10^{11}，M_(Oot)$时变得几乎不变。相应地，<FESC>随着恒星质量的增加而增加，直到Mast，Mot10^8，M0ot，质量越大，<FESC>越小。即使应用单星恒星群合成模型，我们也发现在$Mast\sim 10^8，ModoT}$处有一个中等的<FESC>∼.2。逃逸的电离光子中，近一半来自年龄在1-3岁的恒星，其余的来自年龄在3-10岁的恒星。二进制只有一个温和的影响，使<∼>增加25%-35%，并使逃逸光子的数量增加60%-80%。大多数泄漏的电离光子来自活跃的恒星形成区域，这些区域通常包含一个被致密壳层包围的反馈驱动的KPC级超级气泡。贝壳在加速的同时正在形成恒星，所以在贝壳早期形成的新恒星已经在贝壳内。气泡中和壳层边缘附近的年轻恒星可以完全电离一些通过反馈预先清除的低柱密度路径，允许它们的大部分电离光子逃逸。在高质量端<FESC>的减小是由于尘埃的衰减，而在低质量端<FESC>的减小是由于恒星形成效率低下，从而导致反馈。当质量一定时，<FESC>随红移增大而增大。尽管在我们的模拟中，绝对<FESC>并不完全收敛于分辨率，但<FESC>与质量和红移的关系可能是稳健的。我们的模拟产生了足够的电离光子来进行宇宙再电离。
We present the escape fraction of hydrogen ionizing photons (fesc) from a sample of 34 high-resolution cosmological zoom-in simulations of galaxies at z ≥ 5 in the Feedback in Realistic Environments project, post-processed with a Monte Carlo radiative transfer code for ionizing radiation. Our sample consists of 8500 haloes in Mvir ∼ 108–$10^{12}\, M_{\odot }$ (M* ∼ 104–$10^{10}\, M_{\odot }$) at z = 5–12. We find the sample average 〈fesc〉increases with halo mass for Mvir ∼ 108–$10^{9.5}\, M_{\odot }$, becomes nearly constant for 109.5–$10^{11}\, M_{\odot }$, and decreases at ${\gtrsim}10^{11}\, M_{\odot }$. Equivalently, 〈fesc〉 increases with stellar mass up to $M_{\ast }\sim 10^8\, M_{\odot }$ and decreases at higher masses. Even applying single-star stellar population synthesis models, we find a moderate 〈fesc〉 ∼ 0.2 for galaxies at $M_{\ast }\sim 10^8\, M_{\odot }$. Nearly half of the escaped ionizing photons come from stars 1–3 Myr old and the rest from stars 3–10 Myr old. Binaries only have a modest effect, boosting 〈fesc〉 by ∼25–35 per cent and the number of escaped photons by 60–80 per cent. Most leaked ionizing photons are from vigorously star-forming regions that usually contain a feedback-driven kpc-scale superbubble surrounded by a dense shell. The shell is forming stars while accelerated, so new stars formed earlier in the shell are already inside the shell. Young stars in the bubble and near the edge of the shell can fully ionize some low-column-density paths pre-cleared by feedback, allowing a large fraction of their ionizing photons to escape. The decrease of 〈fesc〉 at the high-mass end is due to dust attenuation, while at the low-mass end, 〈fesc〉 decreases owing to inefficient star formation and hence feedback. At fixed mass, 〈fesc〉 tends to increase with redshift. Although the absolute 〈fesc〉does not fully converge with resolution in our simulations, the mass- and redshift-dependence of 〈fesc〉 is likely robust. Our simulations produce sufficient ionizing photons for cosmic reionization.