Radiative transfer effects on the Lyα forest
Radiative transfer effects on the Lyα forest
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Lyα 森林的辐射传输效应
DOI：
10.1111/j.1365-2966.2005.09682.x
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发表时间：
2005
影响因子：
4.8
通讯作者：
Trieste
中科院分区：
文献类型：
--
作者：
A. Maselli;A. F. Mpa;G. Sissa;Trieste
通过对H I和He II Lyα森林的大量研究以及精确的星系际介质（IGM）金属丰度测量，已经积累了波动紫外线背景（UVB）的强有力的观测证据。UVB波动可能是由电离源的不均匀分布和/或通过间接IGM的辐射传输（RT）引起的。在这项研究中，我们调查，通过数值模拟，RT效应的作用，如阴影，自屏蔽和过滤的电离辐射，在引起波动的UVB。我们专注于可能的可检测的签名，这些影响的量来自Lyα森林光谱，光电离率波动，η（N He II /N HI）参数分布和IGM温度在z 3。我们发现，RT诱导波动高达60%的UVB，这是紧密相关的密度场。由于He II的高不透明度，UVB的平均强度逐渐向更高的密度和4赖德以上的光子能量抑制。过密区（Δ ≥ 5）对宇宙He II电离辐射的屏蔽产生η随过密而减小的趋势。此外，我们还发现，从H i-He n Lyα森林观测中推断出的平均η值只能通过适当地考虑实际的IGM不透明度来解释。我们概述并讨论了我们的研究结果的几个影响。
Strong observational evidence for a fluctuating ultraviolet background (UVB) has been accumulating through a number of studies of the H I and He II Lyα forest as well as accurate intergalactic medium (IGM) metallicity measurements. UVB fluctuations could arise both from the inhomogeneous distribution of the ionizing sources and/or from radiative transfer (RT) through the filamentary IGM. In this study we investigate, via numerical simulations, the role of RT effects, such as shadowing, self-shielding and filtering of the ionizing radiation, in giving rise to a fluctuating UVB. We focus on possible detectable signatures of these effects on quantities derived from Lyα forest spectra, as photoionization rate fluctuations, η(≡N He II /N HI ) parameter distributions and the IGM temperature at z 3. We find that RT induces fluctuations up to 60 per cent in the UVB, which are tightly correlated to the density field. The UVB mean intensity is progressively suppressed toward higher densities and photon energies above 4 Ryd, due to the high He II opacity. Shielding of overdense regions (Δ ≥ 5) from cosmic He II ionizing radiation produces a decreasing trend of η with, overdensity. Furthermore, we find that the mean η value inferred from H i-He n Lyα forest observations can be explained only by properly accounting for the actual IGM opacity. We outline and discuss several implications of our findings.