COBE observations of the cosmic infrared background

Abstract The diffuse infrared background experiment (DIRBE) on the COsmic Background Explorer (COBE) measured the total infrared signal seen from space at a distance of 1 AU from the Sun. Using time variations as the Earth went around the Sun, it is possible to remove most of the foreground signal produced by the interplanetary dust cloud [zodiacal light]. By correlating the DIRBE signal with the column density of atomic hydrogen measured using the 21 cm line, it is possible to remove most of the foreground signal produced by interstellar dust, although one must still be concerned by dust associated with H 2 (molecular gas) and H II (the warm ionized medium). DIRBE was not able to determine the cosmic infrared background (CIRB) in the 5–60 μm wavelength range, but does detect both a far infrared background and a near infrared background. The far infrared background has an integrated intensity of about 34 nW/m 2 /sr, while the near infrared and optical extragalactic background has about 59 nW/m 2 /sr. The far infrared absolute spectrophotometer (FIRAS) on COBE has been used to constrain the long wavelength tail of the far infrared background but a wide range of intensities at 850 μm are compatible with the FIRAS data. Thus the fraction of the CIRB produced by SCUBA sources has large uncertainties in both the numerator and the denominator.