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

The density of the far-infrared/submillimeter (mR/SMM) diffuse extragalacti c radiation field has been determined recently from COBE data. Nearly simul taneously, deep FIR/SMM surveys have detected substantial numbers of optica lly 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 g enerated through nucleosynthesis, most of this energy must have been produc ed at epochs z less than or similar to 2. Hubble Deep Field data cited by M adau, Pozzetti, & Dickinson indicate that the bulk of the integrated extrag alactic background must have been generated even more recently, at z < 1.