标题： 宇宙再电离的计算机模拟：电离背景和平均自由程的演化 显示英文标题

标题： Cosmic Reionization on Computers: The Evolution of Ionizing Background and Mean Free Path

摘要： 再电离末期阶段的观测表明，在$z\approx 5-6$时，电离背景并不均匀且平均自由程（MFP）发生剧烈变化。 由于 MFP 与 Lyman 限制系统和阻尼 Lyman-alpha 系统（LLSs 和 DLAs，即电离光子的“汇”）的分布密切相关，因此理解它们非常重要。 在这项研究中，我们利用了 CROC 模拟，这些模拟既具有足够的空间分辨率以解析星系形成和 LLSs，同时结合了完全耦合的辐射传输来模拟再电离过程。 在我们的分析中，我们将电离背景和 MFP 的演化联系起来。 我们分析了两个具有不同再电离历史的 CROC 盒子，并发现两种模拟中的电离背景分布显示出显著的偏斜度，偏离了对数正态分布。 此外，晚再电离盒中的电离背景在$z\approx5$时仍显示出显著波动（$\sim 40\%$）。 我们还测量了从潜在类星体宿主晕中心 0.15 pMpc 处开始视线方向上的 MFP。 从这些视线方向测得的 MFP 演化表现出一个拐点，该拐点与每个盒子再电离历史中所有中性岛屿消失的时间（盒子再电离历史的“脚踝”）一致。 在没有 LLSs 的情况下，MFP 在$z\approx 5$时会偏高$\approx 20\%$。 我们还将随机视线方向上测得的 MFP 进行了比较。 我们发现，在$z\approx 5$时，从大质量晕中心开始的视线方向上测得的 MFP 比随机视线方向上测得的 MFP 系统性地小$\approx 10\%$。 我们认为这种差异是由于大质量晕 1 pMpc 范围内密集结构的集中效应所致。 我们的研究结果强调了高保真模型在解释观测测量中的重要性。 显示英文摘要

摘要： Observations of the end stages of reionization indicate that at $z\approx 5-6$, the ionizing background is not uniform and the mean free path (MFP) changes drastically. As MFP is closely related to the distribution of Lyman Limit Systems and Damped Lyman-alpha Systems (LLSs and DLAs, or ionizing photon "sinks"), it is important to understand them. In this study, we utilize the CROC simulations, which have both sufficient spatial resolution to resolve galaxy formation and LLSs alongside a fully coupled radiative transfer to simulate the reionization processes. In our analysis, we connect the evolution of the ionizing background and the MFP. We analyze two CROC boxes with distinct reionization histories and find that the distribution of ionizing background in both simulations display significant skewness that deviate from log-normal. Further, the ionizing background in late reionization box still displays significant fluctuations ($\sim 40\%$) at $z\approx5$. We also measure the MFP along sightlines that start 0.15 pMpc away from the center of potential quasar hosting halos. The evolution of the MFP measured from these sightlines exhibits a break that coincides with when all the neutral islands disappear in the reionization history of each box (the `ankle' of the reionization history of the box). In the absence of LLSs, the MFP will be biased high by $\approx 20\%$ at $z\approx 5$. We also compare the MFP measured in random sightlines. We find that at $z\approx 5$ the MFP measured in sightlines that start from massive halos are systematically smaller by $\approx 10\%$ compared with the MFP measured in random sightlines. We attribute this difference to the concentration of dense structures within 1 pMpc from massive halos. Our findings highlight the importance of high fidelity models in the interpretation of observational measurements.