Cosmic InfraRed Background Radiation

The Cosmic InfraRed Background (CIRB) is the radiation from stars in many faint galaxies. It is what is left over after emission from our Solar System and our Galaxy has been subtracted away. Here are pictures of the sky before and after this foreground subtraction. The near-infrared (wavelengths near 2-3 microns) and optical (wavelengths near 500 nm) part of this extragalactic background light is just starlight redshifted into the infrared. But some starlight is absorbed by dust and re-emitted in the far-infrared (wavelengths near 100 microns). The figure below shows the cosmic near-infrared background in blue on the right, the cosmic far-infrared background in green in the middle, and the cosmic microwave background on the left.

graph of nu*J_\nu vs wavelength

The CMB is by far the largest of these radiation fields, with a total intensity of 996 nW/m2/sr. The cosmic far-IR background, which was announced in January 1998, has a total intensity of 39 nW/m2/sr, while the cosmic near-IR background found by Gorjian, Wright & Chary and Wright & Reese has a total intensity of 37 nW/m2/sr. Together these IR backgrounds add up to 8% of the CMB's total intensity.

The black data points on this graph come from the DIRBE experiment on the COBE satellite. The red data points are modified DIRBE results that assume that 37.5% of the 100 micron radiation seen after extrapolating to zero neutral hydrogen column density is due to an error in the zodiacal light model used by Hauser et al.

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© 1999-2000 Edward L. Wright. Last modified 9-May-2000