Absorption in the 21 cm Hydrogen Line at $z>10$ as a Sensitive Tool for the Construction of a Cosmological Model on Small Scales

TL;DR

This paper explores how 21 cm hydrogen line absorption at high redshift can be used to detect features in the primordial density perturbation spectrum, enabling reconstruction of small-scale cosmological models.

Contribution

It demonstrates that 21 cm absorption features can reveal the presence and position of a bump in the density perturbation spectrum at small scales.

Findings

Absorption intensity is affected by early star formation and UV background.

The position of absorption features can indicate the bump in the perturbation spectrum.

Method allows reconstruction of small-scale cosmological perturbations.

Abstract

The cosmic microwave background absorption intensity in the 21 cm line of neutral hydrogen in the presence of additional power in the form of a "bump" in the spectrum of cosmological density perturbations is calculated. The main absorption-amplifying effect is the earlier birth of the first stars forming an ultraviolet radiation background. This radiation reduces the spin temperature of neutral hydrogen and, thus, amplifies the absorption in the 21 cm line. A comparison of various cosmological models (with and without a bump in the density perturbation spectrum) shows that it is possible to determine the probable position of the bump in the perturbation spectrum and, thus, to reconstruct the spectrum of cosmological perturbations on scales $k>1$~Mpc${}^{-1}$ from the position of the absorption frequency profile.