Kavli Affiliate: George Efstathiou
| First 5 Authors: Sudipta Sikder, Rennan Barkana, Anastasia Fialkov, ,
| Summary:
The efficiency of radio emission is an important unknown parameter of early
galaxies at cosmic dawn, as models with high efficiency have been shown to
modify the cosmological 21-cm signal substantially, deepening the absorption
trough and boosting the 21-cm power spectrum. Such models have been previously
directly constrained by the overall extragalactic radio background as observed
by ARCADE-2 and LWA-1. In this work, we constrain the clustering of high
redshift radio sources by utilizing the observed upper limits on
arcminute-scale anisotropy from the VLA at 4.9~GHz and ATCA at 8.7~GHz. Using a
semi-numerical simulation of a plausible astrophysical model for illustration,
we show that the clustering constraints on the radio efficiency are much
stronger than those from the overall background intensity, by a factor that
varies from 12 at redshift 7 to 30 at redshift 22. As a result, the predicted
maximum depth of the global 21-cm signal is lowered by a factor of 5 (to
1700~mK), and the maximum 21-cm power spectrum peak at cosmic dawn is lowered
by a factor of 24 (to $2times 10^5$~mK$^2$). We conclude that the observed
clustering is the strongest current direct constraint on such models, but
strong early radio emission from galaxies remains viable for producing a
strongly enhanced 21-cm signal from cosmic dawn.
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