The earliest galaxies seen in 21 cm line absorption
The earliest galaxies seen in 21 cm line absorption
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DOI：
10.1111/j.1365-2966.2010.17579.x
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发表时间：
2010-09
影响因子：
4.8
通讯作者：
Yidong Xu;A. Ferrara;Xuelei Chen
中科院分区：
文献类型：
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作者：
Yidong Xu;A. Ferrara;Xuelei Chen
我们研究了在再电离早期阶段由非线性结构产生的21厘米的吸收线，即无恒星的微晕和矮星系。在对它们的性质进行了详细的模拟之后，特别是对耦合物理的关注，我们确定了它们的21厘米吸收线轮廓。迷你晕/矮星系周围流入的气体速度强烈地影响着谱线的形状，并且由于系统维里半径外的低自旋温度，产生了角状的谱线轮廓。当视线穿过矮星系的H II区时，矮星系的光学厚度会减小，特别是由具有较高恒星质量和/或重顶初始质量函数的矮星系产生的大H II区会导致光学深度槽而不是吸收线。我们计算了21厘米森林的高红移类星体和伽马射线暴(GRBs)的射电余辉的合成谱。即使有了计划中的平方公里阵列(SKA)，大部分伽玛暴的射电余辉(如果不是全部的话)仍然太暗，不能作为高分辨率(1千赫)观测的背景源，但高z类星体的吸收线很容易被探测到。在没有X射线背景或非常弱的情况下，针对伽玛暴余辉的宽带观测也可以用来揭示来自迷你晕和矮星系的21厘米信号的演变，但如果存在早期的X射线背景，这就变得困难了。因此，21厘米的吸收可能是X射线背景和早期宇宙热历史的存在/强度的有力探测器。
We investigate the 21 cm absorption lines produced by non-linear structures during the early stage of reionization, i.e. the starless minihaloes and the dwarf galaxies. After a detailed modelling of their properties, with particular attention to the coupling physics, we determine their 21 cm absorption line profiles. The infalling gas velocity around minihaloes/dwarf galaxies strongly affects the line shape and, with the low spin temperatures outside the virial radii of the systems, gives rise to horn-like line profiles. The optical depth of a dwarf galaxy is reduced for lines of sight penetrating through its H II region and, especially, a large H II region created by a dwarf galaxy with higher stellar mass and/or a top-heavy initial mass function results in an optical depth trough rather than an absorption line. We compute synthetic spectra of 21 cm forest for both high-redshift quasars and radio afterglows of gamma-ray bursts (GRBs). Even with the planned Square Kilometre Array (SKA), radio afterglows of most if not all GRBs would still be too dim to be the background sources for high-resolution (1 kHz) observations, but absorption lines can be easily detected towards a high-z quasar. Broadband observation against GRB afterglows can also be used to reveal the evolving 21 cm signal from both minihaloes and dwarf galaxies if there was no X-ray background or it was extremely weak, but it becomes difficult if an early X-ray background existed. Hence, the 21 cm absorption could be a powerful probe of the presence/intensity of the X-ray background and the thermal history of the early Universe.