恒星局部辐射对HI柱密度分布的影响
The impact of local stellar radiation on the HI column density distribution
摘要：
人们通常认为，当地的电离辐射源对HI在再电离后宇宙中的分布几乎没有影响。虽然这对于IGM来说是一个很好的假设，但分析论证表明，对于高柱密度吸收体（N_HI > 10^17 /cm ^2），局部源通常可能比背景辐射更重要。我们后处理宇宙学模拟与准确的辐射输运，调查本地恒星源的HI分布的影响。我们表明，有限的数值分辨率和简化处理的ISM是典型的当前宇宙学模拟提供了重大的挑战，但许多问题可以通过采取两个步骤来克服。首先，使用ISM粒子而不是恒星粒子作为源导致源分布的更好的采样。其次，通过重新调整源的光度，使逃逸到IGM的辐射量与产生所观察到的背景所需的一致，许多结果变得不敏感的预测部分的辐射，逃逸的源附近的错误。通过采用这种策略，并通过改变关于未分辨ISM结构的假设，我们得出结论，我们可以稳健地估计柱密度N_HI << 10^21 /cm ^2的局部源的影响。然而，无论是电离辐射的逃逸分数，还是本地源对N_HI >~ 10^21系统丰度的影响，都不能有把握地预测。我们发现，当N_HI <<10 ^17时，恒星局部辐射并不重要，但它会影响莱曼极限和DLA系统。对于10^18 < N_HI < 10^21，局域源的影响随着红移而增加。在z = 5时，N_HI >> 10^17的吸收体的丰度显著降低，但在z = 0时，只有当N_HI >~ 10^21 /cm ^2时，这种降低才变得显著。
英文摘要：
It is often assumed that local sources of ionizing radiation have little impact on the distribution of HI in the post-reionization Universe. While this is a good assumption for the IGM, analytic arguments suggest that local sources may typically be more important than the background radiation for high column density absorbers (N_HI > 10^17 /cm^2). We post-process cosmological simulations with accurate radiation transport to investigate the impact of local stellar sources on the HI distribution. We demonstrate that the limited numerical resolution and the simplified treatment of the ISM that are typical of current cosmological simulations provide significant challenges, but that many of the problems can be overcome by taking two steps. First, using ISM particles rather than stellar particles as sources results in a much better sampling of the source distribution. Second, by rescaling the source luminosities so that the amount of radiation escaping into the IGM agrees with that required to produce the observed background, many of the results become insensitive to errors in the predicted fraction of the radiation that escapes the immediate vicinity of the sources. By adopting this strategy and by varying the assumptions about the structure of the unresolved ISM, we conclude that we can robustly estimate the effect of local sources for column densities N_HI << 10^21 /cm^2. However, neither the escape fraction of ionizing radiation nor the effect of local sources on the abundance of N_HI >~ 10^21 systems can be predicted with confidence. We find that local stellar radiation is unimportant for N_HI << 10^17, but that it can affect Lyman Limit and DLA systems. For 10^18 < N_HI < 10^21 the impact of local sources increases with redshift. At z = 5 the abundance of absorbers with N_HI >> 10^17 is substantially reduced, but at z = 0 the reduction only becomes significant for N_HI >~ 10^21 /cm^2.
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