The Far Infrared and Submillimeter Diffuse Extragalactic

The cosmic infrared background (CIB) radiation was a long-sought fossil of energetic processes associated with structure formation and chemical evolution since the Big Bang. The COBE Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectropho-tometer (FIRAS) were specifically designed to search for this background from 1.25 µm to millimeter wavelengths. These two instruments provided high quality, absolutely calibrated all-sky maps which have enabled the first detections of the CIB, initially at far infrared and submillimeter wavelengths, and more recently in the near infrared as well. The aim of this paper is to review the status of determinations of the CIB based upon COBE measurements. The results show that the energy in the CIB from far infrared to millimeter wavelengths is comparable to that in the integrated light of galaxies from UV to near infrared wavelengths: the universe had a luminous but dusty past. On the assumption that nucle-osynthesis in stars is the energy source for most of this light, the results also imply that 1–8% of cosmic baryons has been converted to helium and heavier elements in stars. The integrated background light from UV to millimeter wavelengths, 60–120 nW m −2 sr −1 , is about 10% of that in the cosmic microwave background. Current knowledge of the CIB provides significant new constraints on models of the history of star formation and galaxy evolution.