Cosmic abundance of iron

Abstract

I explore a possibility to estimate an upper limit of the current iron abundance of the barion matter. The upper limit is determined by the minimal iron abundance, at which the gamma-ray background, produced by the decay of $^{56}$Ni synthesised in the Universe to date, contradicts the observational MeV gamma-ray background. I calculate the gamma-ray background from SNe~Ia and SNe~II with the gamma-ray scattering and absorption in supernova envelope. It is shown that the model background does not contradict the observed MeV background, if the present day iron abundance of the barion matter is less than 15\% of the solar abundance.