21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
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DOI：
10.1093/mnras/stu2512
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发表时间：
2014-06
影响因子：
4.8
通讯作者：
R. Ghara;T. R. Choudhury;K. Datta;K. Datta
中科院分区：
文献类型：
--
作者：
R. Ghara;T. R. Choudhury;K. Datta;K. Datta
21厘米的亮度温度$\delta T_{\rm B}$波动从再电离承诺提供信息的物理过程中，时代。我们提出了一个形式主义的产生$\delta T_{\rm B}$分布使用暗物质模拟和一维辐射传输代码。我们的分析是能够占的自旋温度T_{\rm S}$波动所产生的不均匀的X射线加热和Ly$\alpha$耦合在宇宙黎明。在大尺度下（$k \sim 0.1$ Mpc$^{-1}$），当气体体积分数为10%$时，$\delta T {\rm B}$功率谱幅值达到最大。功率谱在宇宙黎明期间显示出类似“隆起”的特征，其位置测量了加热区域的典型尺寸。我们发现，功率谱上的特殊速度的影响是可以忽略不计的大规模的再电离历史的大部分。在早期阶段（当体积平均电离分数$\lesssim 0.2$），这是因为信号是由$T_{\rm S}$波动为主。对于仅由高质量（$\gtrsim 10 ^9\，\rm M_{\odot}$）晕内的恒星驱动的再电离模型，特殊的速度效应仅在较小的尺度（$k \gtrsim 0. 4 $ Mpc$^{-1}$）下突出，其中中性氢密度的斑块占主导地位。这些结论不受源的X射线谱的振幅或陡度变化的影响。
The 21 cm brightness temperature $\delta T_{\rm b}$ fluctuations from reionization promise to provide information on the physical processes during that epoch. We present a formalism for generating the $\delta T_{\rm b}$ distribution using dark matter simulations and an one-dimensional radiative transfer code. Our analysis is able to account for the spin temperature $T_{\rm S}$ fluctuations arising from inhomogeneous X-ray heating and Ly$\alpha$ coupling during cosmic dawn. The $\delta T_{\rm b}$ power spectrum amplitude at large scales ($k \sim 0.1$ Mpc$^{-1}$) is maximum when $\sim 10\%$ of the gas (by volume) is heated above the CMB temperature. The power spectrum shows a "bump"-like feature during cosmic dawn and its location measures the typical sizes of heated regions. We find that the effect of peculiar velocities on the power spectrum is negligible at large scales for most part of the reionization history. During early stages (when the volume averaged ionization fraction $\lesssim 0.2$) this is because the signal is dominated by fluctuations in $T_{\rm S}$. For reionization models that are solely driven by stars within high mass ($\gtrsim 10^9\, \rm M_{\odot}$) haloes, the peculiar velocity effects are prominent only at smaller scales ($k \gtrsim 0.4$ Mpc$^{-1}$) where patchiness in the neutral hydrogen density dominates the signal. The conclusions are unaffected by changes in the amplitude or steepness in the X-ray spectra of the sources.