Searching for the cosmic infrared background

The cumulative emissions of pregalactic, protogalactic, and evolving galactic systems are expected to be recorded in a cosmic infrared background (CIB). Measurement of such a uniform background in the infrared requires absolute sky brightness measurements from space. The Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE) spacecraft is the first space experiment designed to conduct a systematic search for the CIB from 1.25 to 240 μm, and the COBE Far Infrared Absolute Spectrophotometer (FIRAS) provides additional absolutely calibrated all‐sky measurements from 100 μm to 5 mm wavelengths. With the data from these two experiments in hand, the challenge now becomes discrimination of the bright foreground emissions from interplanetary dust and Galactic sources to reveal the extragalactic background. Conservative limits on the isotropic infrared background are given by the minimum observed sky brightness at each wavelength. Extensive modeling of the foregrounds is under way to isolate or strongly limit the extragalactic infrared component. The current approach to these modeling efforts is described and representative present residuals are reported. Results are compared with those from recent rocket flights and with the extragalactic light estimated from galaxy counts.