The cosmic infrared background radiation, star formation rate, and metallicity

The density of the far-infrared/submillimeter (mR/SMM) diffuse extragalactic radiation field has been determined recently from COBE data. Nearly simultaneously, deep FIR/SMM surveys have detected substantial numbers of optically unidentified sources, which have led to the proposal that galaxies and protogalaxies at redshifts z = 2-4 may account for an appreciable fraction of the background. Here I show that, if the reported radiation levels are generated through nucleosynthesis, most of this energy must have been produced at epochs z less than or similar to 2. Hubble Deep Field data cited by Madau, Pozzetti, & Dickinson indicate that the bulk of the integrated extragalactic background must have been generated even more recently, at z < 1.