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 if the far infrared-radio correlation q ( z ) evolved in time .
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 .