The 21-cm forest as a simultaneous probe of dark matter and cosmic heating history

The 21-cm absorption lines from atomic hydrogen, known as the 21-cm forest, are here proposed to probe simultaneously dark matter particle mass and cosmic heating history. With upcoming observational facilities, the statistical features of the 21-cm forest will constrain the nature of dark matter and the first galaxies at cosmic dawn. The absorption features in spectra of high-redshift background radio sources, caused by hyperfine structure lines of hydrogen atoms in the intervening structures, are known collectively as the 21-cm forest. They provide a unique probe of small-scale structures during the epoch of reionization, and can be used to constrain the properties of the dark matter (DM) thought to govern small-scale structure formation. However, the signals are easily suppressed by heating processes that are degenerate with a warm DM model. Here we propose a probe of both the DM particle mass and the heating history of the Universe, using the one-dimensional power spectrum of the 21-cm forest. The one-dimensional power spectrum measurement not only breaks the DM model degeneracy but also increases the sensitivity, making the probe actually feasible. Making 21-cm forest observations with the upcoming Square Kilometre Array has the potential to simultaneously determine both the DM particle mass and the heating level in the early Universe, shedding light on the nature of DM and the first galaxies.

Automated summary

The 21-cm absorption lines from atomic hydrogen, known as the 21-cm forest, can be used to probe both the mass of dark matter particles and the heating history of the Universe. They provide a unique way to study small-scale structures during reionization and constrain the properties of dark matter. By measuring the one-dimensional power spectrum of the 21-cm forest, we can break the degeneracy in the dark matter model and increase the sensitivity of the probe.