An empirically based calculation of the extragalactic infrared background

Using the excellent observed correlations among various infrared wave bands with 12 and 60 mu m luminosities, we calculate the 2-300 mu m spectra of galaxies as a function of luminosity. We then use 12 mu m and 60 mu m galaxy luminosity functions derived from IRAS data, together with recent data on the redshift evolution of galaxy emissivity, to derive a new, empirically based infrared background spectrum from stellar and dust emission in galaxies. Our best estimate for the infrared background is of order 2-3 nW m(-2) sr(-1) with a peak around 200 mu m reaching similar to 6-8 nW m(-2) sr(-1). Our empirically derived background spectrum is fairly hat in the mid-infrared, as opposed to spectra based on modeling with discrete temperatures that exhibit a pronounced "valley" in the mid-infrared. We also derive a conservative lower limit to the infrared background that is more than a factor of 2 lower than our derived flux.