Misc,
The cosmic radio background from 150 MHz--8.4 GHz, and its division into AGN and star-forming galaxy flux
(2023)cite arxiv:2301.03699.
Abstract
We present a revised measurement of the extra-galactic background light (EBL)
at radio frequencies based on a near complete compendium of radio source
counts. We present the radio-EBL at 150 MHz, 325 MHz, 610 MHz, 1.4 GHz, 3 GHz,
5 GHz, and 8.4 GHz. In all cases the contribution to the radio-EBL, per decade
of flux, exhibits a two-humped distribution well matched to the AGN and
star-forming galaxy (SFG) populations, and with each population contributing
roughly equal energy. Only at 3 GHz are the source count contributions to the
EBL fully convergent, and hence we report empirical lower limits to the
radio-EBL in the remaining bands. Adopting predictions from the SHARK
semi-analytic model for the form of the SFG population, we can fit the fainter
source counts providing measurements of the total contribution to the radio-EBL
for the SFG and the AGN populations separately. This constitutes an empirically
constrained model-dependent measurement for the SFG contribution, but a fully
empirical measurement of the AGN contribution. Using the ProSpect
spectral energy distribution code we can model the UV-optical-infrared-mm-radio
SFG EBL at all frequencies from the cosmic star-formation history and the
adoption of a Chabrier initial mass function. However, significant discrepancy
remains ($5\times$) between our source-count estimates of the radio-EBL and the
direct measurements reported from the ARCADE-2 experiment. We can rule out a
significant missing discrete source radio population and suggest that the cause
of the high ARCADE-2 radio-EBL values may need to be sought either in the
foreground subtraction or as a yet unknown diffuse component in the radio sky.
