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تسجيل مستخدم جديدLyman-$alpha$ coupling and heating at Cosmic Dawn
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Shikhar Mittal
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The global 21-cm signal from the cosmic dawn is affected by a variety of heating and cooling processes. We investigate the impact of heating due to Lyman-$alpha$ (Ly~$alpha$) photons on the global 21-cm signal at cosmic dawn using an analytical expression of the spectrum around the Ly~$alpha$ resonance based on the so-called `wing approximation. We derive a new expression for the scattering correction and for the first time give a simple close-form expression for the cooling due to injected Ly~$alpha$ photons. We perform a short parameter study by varying the Ly~$alpha$ background intensity by four orders of magnitude and establish that a strong Ly~$alpha$ background is necessary, although not sufficient, in order to reproduce the recently detected stronger-than-expected 21-cm signal by the EDGES Collaboration. We show that the magnitude of this Ly~$alpha$ heating is smaller than previously estimated in the literature by two orders of magnitude or more. As a result, even a strong Ly~$alpha$ background is consistent with the EDGES measurement. We also provide a detailed discussion on different expressions of the Ly~$alpha$ heating rate used in the literature.
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