Integrated far-infrared background from galaxies

Abstract

We assess the general possibility of detecting the integrated background radiation from galaxies at far-infrared wavelengths. We adopt the analytical solutions for the evolution of the far-infrared luminosity of galaxies obtained by Wang and calculate the luminosity density from galaxies in the far-infrared, using simple models of galaxy formation. Consistent with the luminosity function at 60 micron determined by IRAS observations, the integrated far-infrared background from galaxies is found to peak at around 100-130 microns, with total radiation density from 0.5% to 6% of the cosmic microwave background. It is found that, in general, early galaxy formation predicts strong far-infrared background and that the chemical evolution dictated by the initial enrichment model leads to stronger far-infrared radiation from galaxies than does the accretion model. We calculate deviations due to galaxies at submillimeter wavelengths from the blackbody spectrum of the cosmic microwave background radiation. In terms of variation in the blackbody temperature, we find δT_CMB_/T_CMB_ = (0.5-2) x 10^-2^ at 0.4 mm. The autocorrelation of fluctuations in the far-infrared background due to the galaxy clustering is calculated, as is the contribution from the far-infrared background to the anisotropy at wavelengths dominated by the cosmic microwave background. The deviation predicted by our calculations in the spectrum and isotropy of the background radiation due to galaxies at far-infrared and submillimeter wavelengths exceeds the designed sensitivity of DIRBE and FIRAS aboard COBE. Therefore, COBE should be able to provide strong tests for the models presented here.