The theoretical implications of the current FIRAS limits on the cosmic infrared background are discussed by Mather at this Symposium and by Wright et al. (1994). The implications of the more general infrared background limits are discussed by Lonsdale at this Symposium. To put the present observational status into the historical context introduced at the beginning of this talk, the upper limits of Table 1 yield an upper limit to the integrated infrared background from 1 to 300 µm of 5 µW m-2 sr-1, still a factor of 5 larger than the integrated CMBR. Table 1 shows that this limit on the CIBR integral is dominated by the thermal emission peak from the interplanetary dust at 12 and 25 µm. Careful modeling of the sky brightness contribution from the interplanetary dust cloud will substantially reduce the limit on the integrated infrared background. However, limits on the CIBR will clearly remain relatively weak in the spectral decade from about 6 to 60 µm until measurements can be made from outside the interplanetary dust cloud.
Measurement of the cosmic infrared background radiation will enhance our understanding of the epoch between decoupling and galaxy formation. The high quality and extensive new measurements of the absolute infrared sky brightness obtained with the DIRBE and FIRAS instruments on the COBE mission are allowing a definitive search for this elusive background, limited primarily by the difficulty of distinguishing it from bright astrophysical foregrounds.
The author gratefully acknowledges the contributions to this report by the many participants in the COBE Project, to his colleagues on the COBE Science Working Group, and especially the many scientists, analysts, and programmers engaged in the DIRBE investigation. The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the COBE. Scientific guidance is provided by the COBE Science Working Group. GSFC is also responsible for the development of the analysis software and for the production of the mission data sets.