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arXiv 1702.00409astro-ph.COastro-ph.GA
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高质量X射线双星和宇宙21厘米信号:宿主星系吸收的影响

High Mass X-ray Binaries and the Cosmic 21-cm Signal: Impact of Host Galaxy Absorption

Arpan Das, Andrei Mesinger, Andrea Pallottini, Andrea Ferrara, John H. Wise

摘要:

通过在再电离之前加热星系际介质(IGM),X射线有望在早期宇宙中发挥重要作用。来自这个“加热时代”(EoH)的宇宙21厘米信号可以作为第一个星系内部高能过程的干净探测器。在这里,我们改进了先前的估计,这个信号,通过使用高分辨率的流体动力学模拟计算的X射线吸收由于星际介质(ISM)的主机星系。在宿主星系内部吸收的X射线无法逃逸到IGM中,并对EoH做出贡献。我们发现,通过这些星系的X射线不透明度可以用一个无金属的ISM来近似,其典型的柱密度为log[N / cm^-2] = 21.4 +0.40-0.65。我们通过将这些ISM不透明度与高质量X射线双星(被认为是早期宇宙中重要的X射线源)的公共光谱相结合来计算得到的21厘米信号。我们的研究结果支持“标准方案”,其中IGM的X射线加热是不均匀的,并发生在大部分再电离之前。大尺度(k ~ 0.1/Mpc)的21 cm功率在z = 10 - 15时达到峰值,约为100 mK^2,红移取决于宇宙恒星形成的历史。这与最近的一些工作相反,这些工作的动机是银河系内部对本地HMXB的X射线吸收要大得多。我们的主要结果可以重现近似的X射线发射HMXB与能量指数α = 1,截断在能量低于0.5千电子伏的幂律谱。

英文摘要:

By heating the intergalactic medium (IGM) before reionization, X-rays are expected to play a prominent role in the early Universe. The cosmic 21-cm signal from this "Epoch of Heating" (EoH) could serve as a clean probe of high-energy processes inside the first galaxies. Here we improve on prior estimates of this signal by using high-resolution hydrodynamic simulations to calculate the X-ray absorption due to the interstellar medium (ISM) of the host galaxy. X-rays absorbed inside the host galaxy are unable to escape into the IGM and contribute to the EoH. We find that the X-ray opacity through these galaxies can be approximated by a metal-free ISM with a typical column density of log[N / cm^-2] = 21.4 +0.40-0.65. We compute the resulting 21-cm signal by combining these ISM opacities with public spectra of high-mass X-ray binaries (thought to be important X-ray sources in the early Universe). Our results support "standard scenarios" in which the X-ray heating of the IGM is inhomogeneous, and occurs before the bulk of reionization. The large-scale (k ~ 0.1/Mpc) 21-cm power reaches a peak of ~100 mK^2 at z = 10 - 15, with the redshift depending on the cosmic star formation history. This is in contrast to some recent work, motivated by the much larger X-ray absorption towards local HMXBs inside the Milky Way. Our main results can be reproduced by approximating the X-ray emission from HMXBs with a power-law spectrum with energy index alpha = 1, truncated at energies below 0.5 keV.

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