Stages of Reionization as Revealed by the Minkowski Functionals
Stages of Reionization as Revealed by the Minkowski Functionals
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DOI：
10.3847/1538-4357/ab43e6
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发表时间：
2018-12
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影响因子：
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通讯作者：
Zhaoting Chen;Yidong Xu;Yougang Wang;Xuelei Chen
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作者：
Zhaoting Chen;Yidong Xu;Yougang Wang;Xuelei Chen
我们研究了再电离时期（EoR）的氢电离场的演化，使用数值模拟。通过计算21 cm亮温场的Minkowski泛函，定量描述了中性区和电离区的拓扑结构，发现再电离过程可分为5个阶段，每个阶段具有不同的拓扑结构，对应于孤立的电离区（“气泡”）;连接的电离区域（“电离纤维”），渗透通过宇宙体积;一个海绵状的配置与交织的中性和电离区后，重叠的气泡;连接的中性区域（“中性纤维”），当电离区域开始包围剩余的中性区域时;和孤立的中性区域（“岛屿”），在整个空间被电离之前，除了星系和微晕中罕见的致密团块，再电离过程完成。我们使用的MF和离子化或中性区域的尺寸统计来区分这些不同的阶段，并找到中性的分数，在该过渡的不同阶段发生。在再电离的后期阶段，中性区比电离区更加孤立，这是再电离岛模型描述的动机。我们比较了岛模型和气泡模型中的后期拓扑演化，表明在岛模型中，由于电离背景，中性纤维更容易破碎成多个碎片。
We study the evolution of the hydrogen ionization field during the epoch of reionization (EoR) using seminumerical simulations. By calculating the Minkowski functionals (MFs) of the 21 cm brightness temperature field, which provides a quantitative description of topology of the neutral and ionized regions, we find that the reionization process can be divided into five stages, each with different topological structures, corresponding to isolated ionized regions (“bubbles”); connected ionized regions (“ionized fibers”) that percolate through the cosmic volume; a sponge-like configuration with intertwined neutral and ionized regions after the overlap of bubbles; connected neutral regions (“neutral fibers”), when the ionized region begins to surround the remaining neutral region; and isolated neutral regions (“islands”), before the whole space is ionized except for the rare dense clumps in galaxies and minihalos and the reionization process is completed. We use the MFs and the size statistics on the ionized or neutral regions to distinguish these different stages and find the neutral fractions at which the transitions of the different stages occur. At the later stages of reionization the neutral regions are more isolated than the ionized regions; this is the motivation for the island model description of reionization. We compare the late-stage topological evolution in the island model and the bubble model, showing that in the island model the neutral fibers are more easily broken into multiple pieces owing to the ionizing background.