电离层中HI对再电离期21厘米强度起伏的影响
The Impact of HI in Galaxies on 21-cm Intensity Fluctuations During the Reionisation Epoch
摘要：
我们调查的影响中性氢（HI）在星系的21厘米波动的统计分析和半数值模拟。随着氢的再电离，宇宙中的HI含量主要由阻尼吸收系统（DLAs）控制，HI中的宇宙密度被观察到在z~1到z~5的宇宙重子密度的约2%的水平上保持恒定。我们表明，外推到再电离时代的结果在一个范围内的空间尺度的21厘米波动的幅度减少了10-20%，这一常数部分。在再电离时代的不同百分比的假设结果在21厘米波动幅度成比例的变化。我们发现，考虑HI在星系/DLAs减少突出的HII区域引起的肩膀在21厘米功率谱（PS），并因此修改的尺度依赖性的21厘米波动。我们还估计了21厘米星系十字PS，并表明十字PS改变相应的HII区域的尺度上的符号。从考虑即将到来的低频阵列的灵敏度，我们发现，HI在星系/DLAs的21厘米波动的统计数据的影响将是显着的PS或交叉PS测量的精度。此外，由于过于密集的区域首先被再电离，我们证明了星系之间的互相关和21厘米的发射变化标志着再电离时代的结束，提供了另一种途径来确定再电离的结束。我们的分析的总和表明，HI内容的星系，再电离的宇宙将需要考虑在详细的建模的21厘米强度PS，以正确地解释测量从即将到来的低频阵列。
英文摘要：
We investigate the impact of neutral hydrogen (HI) in galaxies on the statistics of 21-cm fluctuations using analytic and semi-numerical modelling. Following the reionisation of hydrogen the HI content of the Universe is dominated by damped absorption systems (DLAs), with a cosmic density in HI that is observed to be constant at a level equal to ~2% of the cosmic baryon density from z~1 to z~5. We show that extrapolation of this constant fraction into the reionisation epoch results in a reduction of 10-20% in the amplitude of 21-cm fluctuations over a range of spatial scales. The assumption of a different percentage during the reionisation era results in a proportional change in the 21-cm fluctuation amplitude. We find that consideration of HI in galaxies/DLAs reduces the prominence of the HII region induced shoulder in the 21-cm power spectrum (PS), and hence modifies the scale dependence of 21-cm fluctuations. We also estimate the 21cm-galaxy cross PS, and show that the cross PS changes sign on scales corresponding to the HII regions. From consideration of the sensitivity for forthcoming low-frequency arrays we find that the effects of HI in galaxies/DLAs on the statistics of 21-cm fluctuations will be significant with respect to the precision of a PS or cross PS measurement. In addition, since overdense regions are reionised first we demonstrate that the cross-correlation between galaxies and 21-cm emission changes sign at the end of the reionisation era, providing an alternative avenue to pinpoint the end of reionisation. The sum of our analysis indicates that the HI content of the galaxies that reionise the universe will need to be considered in detailed modelling of the 21-cm intensity PS in order to correctly interpret measurements from forthcoming low-frequency arrays.
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