Speaker
Description
Several ongoing and upcoming radio telescopes are aiming for a detection of either the all sky-averaged (global) 21-cm signal or the 21-cm power spectrum. The extragalactic radio background, as detected by ARCADE-2 and LWA-1, can significantly affect the cosmological 21-cm signal. Such a radio background could have been produced by high-redshift galaxies. We perform a complete calculation that accounts for the fact that the 21-cm absorption occurs along the line of sight, and is therefore sensitive to radio sources lying behind each absorbing cloud. We find that the complete calculation strongly enhances the 21-cm power spectrum during cosmic dawn. Furthermore, using this model, we constrain the clustering of high-redshift radio sources based on observed upper limits from the VLA and ATCA. The results show significantly stronger clustering constraints on radio efficiency compared to those from overall background intensity. Consequently, the predicted maximum depth of the global 21-cm signal and the maximum 21-cm power spectrum peak at cosmic dawn are both lowered. In conclusion, observed clustering stands as the strongest current direct constraint on such models.
