Observations of local star forming galaxies have revealed a correlation between the rate at which galaxies form stars and their X-Ray luminosity .
We combine this correlation with the most recent observational constraints on the integrated star formation rate density , and find that star forming galaxies account for 5-20 % of the total soft and hard X-ray backgrounds , where the precise number depends on the energy band and the assumed average X-ray spectral energy distribution of the galaxies below \sim 20 keV .
If we combine the L _ { X } -SFR relation with recently derived star formation rate function , then we find that star forming galaxies whose X-ray flux falls well ( more than a factor of 10 ) below the detection thresholds of the Chandra Deep Fields , can fully account for the unresolved soft X-ray background , which corresponds to \sim 6 \% of its total .
Motivated by this result , we put limits on the allowed redshift evolution of the parameter c _ { X } \equiv L _ { X } /SFR , and/or its evolution towards lower and higher star formation rates .
If we parametrize the redshift evolution of c _ { X } \propto ( 1 + z ) ^ { b } , then we find that b \leq 1.3 ( 95 % CL ) .
On the other hand , the observed X-ray luminosity functions ( XLFs ) of star forming galaxies indicate that c _ { X } may be increasing towards higher redshifts and/or higher star formation rates at levels that are consistent with the X-ray background , but possibly at odds with the locally observed L _ { X } -SFR relation .