Formation of the hydrogen line 21-cm in Dark Ages and Cosmic Dawn: dependences on cosmology and first light

Abstract

We analyse the formation of the redshifted hyperfine structure line 21-cm of hydrogen atom in the Dark Ages, Cosmic Dawn, and Reionization epochs. The evolution of the global differential brightness temperature in this line was computed to study its dependence on the values of cosmological parameters and physical conditions in the intergalactic medium. Variations of the depth of the Dark Ages absorption line at z ∼ 80 with variations of the cosmological parameters Ωb, Ωcdm, ΩΛ, ΩK, and H0 are studied. The standard model with post-Planck parameters predicts a value of the differential brightness temperature in the centre of the absorption line ∼30–50 mK. The profile of this line can be quite another in the non-standard cosmological models, which include the annihilating or decaying dark matter, a primordial stochastic magnetic field, etc. It can be shallower or be an emission bump instead of an absorption trough. It is also shown that the position and depth of the Cosmic Dawn absorption line formed at 10 < z < 30, due to the Wouthuysen–Field effect, is mainly defined by the spectral energy distribution of the first sources of light. If reionization occurs at zri = 7 ± 1, then the differential brightness temperature in the centre of this line is ∼80 mK. During the reionization, the emission with an amplitude of ∼20 mK is possible. It is also shown that the temperature, density, and degree of ionization of the baryonic component are decisive in calculating the intensity of the 21-cm absorption/emission line from these epochs.

Tackling the Challenges in the 21 cm Global Spectrum Experiment: The Impact of Ionosphere and Beam Distortion

“…The global 21 cm signal originating from cosmic neutral hydrogen is regarded as one of the most promising tools to study the early formation of the structure of the Universe. Detecting this signal holds the potential to unveil crucial insights into the timeline and physical process of Cosmic Dawn and the Epoch of Reionization (EoR; Madau et al 1997;Pritchard & Loeb 2008;Cohen et al 2018), including the properties of the first stars and galaxies, astrophysical feedback processes (Tozzi et al 2000a;Chen & Miralda-Escudé 2004;Barkana 2018;Mebane et al 2020), the nature of dark matter (Dvorkin et al 2014;Tashiro et al 2014;Lopez-Honorez et al 2016;Mondal et al 2024), cosmological parameters, and fundamental physics (Tozzi et al 2000b;Aristizabal Sierra & Fong 2018;Novosyadlyj et al 2023).…”