An Empirically Based Calculation of the Extragalactic Infrared Background

Abstract

Using the excellent observed correlations among various infrared wave bands with 12 and 60 μm luminosities, we calculate the 2-300 μm spectra of galaxies as a function of luminosity. We then use 12 μm and 60 μm 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 μm reaching ∼6-8 nW m-2 sr-1. Our empirically derived background spectrum is fairly flat 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. © 1998. The American Astronomical Society. All rights reserved.