The COBE Diffuse Infrared Background Experiment search for the cosmic infrared background. II. Model of the interplanetary dust cloud

The COBE Diffuse Infrared Background Experiment (DIRBE) was designed to sea rch for the cosmic infrared background (CIB) radiation. For an observer con fined to the inner solar system, scattered light and thermal emission from the interplanetary dust (IPD) are major contributors to the diffuse sky bri ghtness at most infrared wavelengths. Accurate removal of this zodiacal lig ht foreground is a necessary step toward a direct measurement of the GIB. T he zodiacal light foreground contribution in each of the 10 DIRBE wavelengt h bands ranging from 1.25 to 240 mu m is distinguished by its apparent seas onal variation over the whole sky. This contribution has been extracted by fitting the brightness calculated from a parameterized physical model to th e time variation of the all-sky DIRBE measurements over 10 months of liquid He cooled observations. The model brightness is evaluated as the integral along the line of sight of the product of a source function and a three-dim ensional dust density distribution function. The dust density distribution is composed of multiple components: a smooth cloud, three asteroidal dust b ands, and a circumsolar ring near 1 AU. By using a directly measurable quan tity that relates only to the IPD cloud, we exclude other contributors to t he sky brightness from the IPD model. High-quality maps of the infrared sky with the zodiacal foreground removed have been generated using the IPD mod el described here. Imperfections in the model reveal themselves as low-leve l systematic artifacts in the residual maps that correlate with components of the IPD. The most evident of these artifacts are located near the eclipt ic plane in the mid-IR and are less than 2% of the zodiacal foreground brig htness. Uncertainties associated with the model are discussed, including im plications for the CIB search.