21cm Forest with the SKA

TL;DR

The paper explores the potential of SKA1-low to detect 21cm absorption features from the early universe, providing insights into small-scale structures and thermal history during redshifts 7.5-15.

Contribution

It demonstrates how SKA1-low can be used to detect the 21cm forest, offering a new method to study small-scale HI structures and the thermal evolution of the early universe.

Findings

SKA1-low could detect 21cm forest features at z=7.5-15.

The 21cm forest probes small-scale HI density fluctuations.

It can reveal the IGM temperature and heating history.

Abstract

An alternative to both the tomography technique and the power spectrum approach is to search for the 21cm forest, that is the 21cm absorption features against high-z radio loud sources caused by the intervening cold neutral intergalactic medium (IGM) and collapsed structures. Although the existence of high-z radio loud sources has not been confirmed yet, SKA-low would be the instrument of choice to find such sources as they are expected to have spectra steeper than their lower-z counterparts. Since the strongest absorption features arise from small scale structures (few tens of physical kpc, or even lower), the 21cm forest can probe the HI density power spectrum on small scales not amenable to measurements by any other means. Also, it can be a unique probe of the heating process and the thermal history of the early universe, as the signal is strongly dependent on the IGM temperature. Here we show what SKA1-low could do in terms of detecting the 21cm forest in the redshift range z = 7.5-15.