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The 21-cm Background from the Cosmic Dark Ages: Minihalos and the Intergalactic Medium before Reionization

Kyungjin Ahn·Paul R. Shapiro·Marcelo A. Alvarez·Ilian T. Iliev·Hugo Martel·Dongsu Ryu
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Abstract

The H atoms inside minihalos (i.e. halos with virial temperatures T_vir < 10^4 K, in the mass range roughly from 10^4 M_sun to 10^8 M_sun) during the cosmic dark ages in a LCDM universe produce a redshifted background of collisionally-pumped 21-cm line radiation which can be seen in emission relative to the cosmic microwave background (CMB). Previously, we used semi-analytical calculations of the 21-cm signal from individual halos of different mass and redshift and the evolving mass function of minihalos to predict the mean brightness temperature of this 21-cm background and its angular fluctuations. Here we use high-resolution cosmological N-body and hydrodynamic simulations of structure formation at high redshift (z > 8) to compute the mean brightness temperature of this background from both minihalos and the intergalactic medium (IGM) prior to the onset of Ly-alpha radiative pumping. We find that the 21-cm signal from gas in collapsed, virialized minihalos dominates over that from the diffuse shocked gas in the IGM.

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Kyungjin Ahn, Paul R. Shapiro, Marcelo A. Alvarez, Ilian T. Iliev, Hugo Martel, Dongsu Ryu. 2005-09-21. The 21-cm Background from the Cosmic Dark Ages: Minihalos and the Intergalactic Medium before Reionization. https://doi.org/10.1016/j.newar.2005.11.021

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