Detection of the Cosmic Infrared Background at 2.2 and 3.5 Microns Using DIRBE Observations

We compare data from the Diffuse Infrared Background Experiment (DIRBE) on COBE to the model of the infrared sky provided by Wainscoat and colleagues in 1992. The model is first compared with broadband K (2.2 μm) star counts. Its success at K band lends credence to its physical approach, which is extrapolated to the L band (3.5 μm). We have analyzed the histograms of the pixel-by-pixel intensities in the 2.2 and 3.5 μm maps from DIRBE after subtracting the zodiacal light. The shape of these histograms agrees quite well with the histogram shape predicted using the Wainscoat model of the infrared sky, but the predicted histograms must be displaced by a constant intensity in order to match the data. This shift is the cosmic infrared background, which is 16.9 ± 4.4 kJy sr^-1 or 23.1 ± 5.9 nW m^-2 sr^-1 at 2.2 μm and 14.4 ± 3.7 kJy sr^-1 or 12.4 ± 3.2 nW m^-2 sr^-1 at 3.5 μm. Combining our near-IR results with the far-IR background detected by Hauser and colleagues in 1998 suggests that roughly half of the radiation produced by galaxies is absorbed by dust and reradiated in the far-IR.