The contribution of star-forming galaxies to the cosmic radio background

TL;DR

This paper investigates whether star-forming galaxies can explain the cosmic radio background and finds they contribute only about 13%, suggesting other sources are needed.

Contribution

It introduces a model linking the far infrared-radio correlation evolution to the cosmic star formation rate to estimate galaxy radio emission.

Findings

Star-forming galaxies account for only ~13% of the cosmic radio background.

The far infrared-radio correlation evolves with redshift as modeled.

Other sources must contribute significantly to the radio background.

Abstract

Recent measurements of the temperature of the sky in the radio band, combined with literature data, have convincingly shown the existence of a cosmic radio background with an amplitude of $\sim 1$ K at 1 GHz and a spectral energy distribution that is well described by a power law with index $\alpha \simeq -0.6$. The origin of this signal remains elusive, and it has been speculated that it could be dominated by the contribution of star-forming galaxies at high redshift \change{if the far infrared-radio correlation $q(z)$ evolved} in time. \change{We fit observational data from several different experiments by the relation $q(z) \simeq q_0 - \beta \log(1+z)$ with $q_0 = 2.783 \pm 0.024$ and $\beta = 0.705 \pm 0.081$ and estimate the total radio emission of the whole galaxy population at any given redshift from the cosmic star formation rate density at that redshift. It is found that} star-forming galaxies can only account for $\sim$13 percent of the observed intensity of the cosmic radio background.