The subtlety of Ly α photons: changing the expected range of the 21-cm signal
The subtlety of Ly α photons: changing the expected range of the 21-cm signal
复制标题
Ly α 光子的微妙之处：改变 21 厘米信号的预期范围
DOI：
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发表时间：
2021
影响因子：
4.8
通讯作者：
R. Barkana
中科院分区：
文献类型：
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作者：
I. Reis;A. Fialkov;R. Barkana
我们在一个升级的模型中描述了从宇宙黎明到再电离纪元的21厘米信号的演化，其中包括了Lyα辐射的三个微妙效应：Lyα加热、CMB加热(由Lyα光子介导)和Lyα光子的多次散射。考虑到这些影响，我们探索了广泛的天体物理模型，并量化了这些过程对全球21厘米信号及其功率谱的影响。我们发现，在弱X射线加热的模型中，Lyα加热使气体温度升高了高达数学量的{O}(100)$度(CMB加热增加了几度)，从而抑制了预测的21厘米信号。广泛地改变天体物理参数，试图覆盖所有可能的模型范围，我们发现在升级的模型中，全球信号的吸收谷在红移z−15≈19时达到了−165mK的最低可能底值。这与对纯绝热冷却宇宙的预测相反，在纯绝热冷却的宇宙中，最深的可能吸收是宇宙时间的单调递减函数，在z=19时为−178mK，在z=15时为−216mK，在较低的红移时下降到更低的值。在计入Lyα和CMB加热的情况下，我们还观察到了低红移功率谱的强烈抑制，在z=9和k=0.1Mpc−1时，最大可能功率(通过模型系综估计)衰减了6.6倍。最后，我们发现在对应于宇宙黎明的高红移时，Lyα光子的多重散射导致所有模型的功率谱放大了∼2−3倍。
We present the evolution of the 21-cm signal from cosmic dawn and the epoch of reionization (EoR) in an upgraded model including three subtle effects of Ly α radiation: Ly α heating, CMB heating (mediated by Ly α photons), and multiple scattering of Ly α photons. Taking these effects into account we explore a wide range of astrophysical models and quantify the impact of these processes on the global 21-cm signal and its power spectrum. We find that Ly α heating raises the gas temperature by up to $mathcal {O}(100)$ degrees (CMB heating adds a few more degrees) in models with weak X-ray heating, thus suppressing the predicted 21-cm signals. Varying the astrophysical parameters broadly in an attempt to cover the full plausible range of models, we find that in the upgraded model the absorption trough of the global signal reaches a lowest possible floor of −165 mK at redshifts z ≈ 15 − 19. This is in contrast with the predictions for a pure adiabatically cooling Universe, for which the deepest possible absorption is a monotonically decreasing function of cosmic time and is −178 mK at z = 19 and −216 mK at z = 15, dropping to even lower values at lower redshifts. With Ly α and CMB heating included we also observe a strong suppression in the low-redshift power spectra, with the maximum possible power (evaluated over the ensemble of models) attenuated by a factor of 6.6 at z = 9 and k = 0.1 Mpc−1. Finally, we find that at high redshifts corresponding to cosmic dawn, the multiple scattering of Ly α photons leads to an amplification of the power spectrum by a factor of ∼2 − 3 in all models.