第一批恒星产生的21厘米波动的丰富复杂性
The rich complexity of 21-cm fluctuations produced by the first stars
摘要：
我们探讨了红移范围z = 7-40的21厘米信号的完整历史。这个红移范围包括与原始恒星形成有关的宇宙演化的各个时期，并且应该可以被现有或计划中的低频射电望远镜所获得。我们使用半数值计算的方法来探索波动信号的波数在0.03和1 Mpc之间的$^{-1}$，占不均匀的背景的Ly- $α$，X射线，莱曼-维尔纳和电离辐射。我们专注于最近注意到的期望加热占主导地位的硬X射线光谱从高质量的X射线双星。我们研究由此产生的延迟宇宙加热和气体温度波动的抑制，允许在最小的晕质量，有助于恒星形成的大的变化。我们表明，在观测中检测到的加热峰的波数应该告诉我们所发射光子的特征平均自由程和光谱，从而提供关键线索的性质的源加热原始宇宙。我们还考虑了视线的各向异性，它允许额外的信息被提取的21厘米的信号。例如，宇宙气体被加热到宇宙微波背景的温度时的加热跃迁，应该由一个特别各向同性的功率谱清楚地标记出来。更一般地，附加的交叉功率分量$P_X$直接探测哪些源主导21厘米波动。特别是，在宇宙再电离期间（以及在刚刚提到的加热跃迁之后），$P_X$在电离涨落主导的尺度上是负的，而在温度涨落主导的尺度上是正的。
英文摘要：
We explore the complete history of the 21-cm signal in the redshift range z = 7-40. This redshift range includes various epochs of cosmic evolution related to primordial star formation, and should be accessible to existing or planned low-frequency radio telescopes. We use semi-numerical computational methods to explore the fluctuation signal over wavenumbers between 0.03 and 1 Mpc$^{-1}$, accounting for the inhomogeneous backgrounds of Ly-$α$, X-ray, Lyman-Werner and ionizing radiation. We focus on the recently noted expectation of heating dominated by a hard X-ray spectrum from high-mass X-ray binaries. We study the resulting delayed cosmic heating and suppression of gas temperature fluctuations, allowing for large variations in the minimum halo mass that contributes to star formation. We show that the wavenumbers at which the heating peak is detected in observations should tell us about the characteristic mean free path and spectrum of the emitted photons, thus giving key clues as to the character of the sources that heated the primordial Universe. We also consider the line-of-sight anisotropy, which allows additional information to be extracted from the 21-cm signal. For example, the heating transition at which the cosmic gas is heated to the temperature of the cosmic microwave background should be clearly marked by an especially isotropic power spectrum. More generally, an additional cross-power component $P_X$ directly probes which sources dominate 21-cm fluctuations. In particular, during cosmic reionization (and after the just-mentioned heating transition), $P_X$ is negative on scales dominated by ionization fluctuations and positive on those dominated by temperature fluctuations.
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