标题： IslandFAST：模拟再电离晚期的半数值工具 显示英文标题

标题： IslandFAST: A Semi-numerical Tool for Simulating the Late Epoch of Reionization

摘要： 我们介绍了半数值模拟算法和主要结果，即islandFAST，它源自21cmFAST，专为再电离晚期阶段设计。 islandFAST预测大尺度低密度中性区域（中性岛屿）的演化和尺寸分布，并发现再电离晚期（EoR）进行得非常迅速，在每个红移下表现出中性岛屿的特征尺度。 利用islandFAST，我们比较了两种吸收系统对再电离过程的影响，即大尺度低密度中性岛屿与小尺度高密度吸收体。 中性岛屿主导电离场的形态，而小尺度吸收体主导电离光子的平均自由程，并且会延迟和延长再电离过程。 通过我们的半数值模拟，可以在给定小尺度吸收体模型的情况下自洽地推导出电离背景的演化。 在致密吸收体存在的情况下，电离背景的氢电离率降低了数量级。 显示英文摘要

摘要： We present the algorithm and main results of our semi-numerical simulation, islandFAST, which is developed from the 21cmFAST and designed for the late stage of reionization. The islandFAST predicts the evolution and size distribution of the large scale under-dense neutral regions (neutral islands), and we find that the late Epoch of Reionization (EoR) proceeds very fast, showing a characteristic scale of the neutral islands at each redshift. Using islandFAST, we compare the impact of two types of absorption systems, i.e. the large scale under-dense neutral islands versus small scale over-dense absorbers, in regulating the reionization process. The neutral islands dominate the morphology of the ionization field, while the small scale absorbers dominate the mean free path of ionizing photons, and also delay and prolong the reionization process. With our semi-numerical simulation, the evolution of the ionizing background can be derived self-consistently given a model for the small absorbers. The hydrogen ionization rate of the ionizing background is reduced by an order of magnitude in the presence of dense absorbers.