In a companion paper to our X-ray binary paper, we calculated the expected 21-cm signal (Wikipedia) from a strongly clustered group of galaxies at redshift 15 when the universe was only 300 Myr old. Here we make predictions for the SKA radio observatory, which could possibly probe the heating and ionization caused by UV and X-ray sources within the first galaxies. In this paper, we show that in some circumstances it will be possible to determine from SKA observations whether X-ray sources had a significant impact on the surrounding intergalactic medium, constraining the earliest population of stars and their remnants in the first galaxies.

Image credit: SKA