The COBE diffuse infrared background experiment search for the Cosmic Infrared Background. III. Separation of galactic emission from the infrared skybrightness

The Cosmic Infrared Background (CIB) is hidden behind veils of foreground e mission from our own solar system and Galaxy. This paper describes procedur es for removing the Galactic IR emission from the 1.25-240 mu m COBE DIRBE maps as steps toward the ultimate goal of detecting the GIB. The Galactic e mission models are carefully chosen and constructed so that the isotropic C IB is completely retained in the residual sky maps. We start with DIRBE dat a from which the scattered light and thermal emission of the interplanetary dust (IPD) cloud have already been removed. Locations affected by the emis sion from bright compact and stellar sources are excluded from the analysis . The unresolved emission of faint stars at near- and mid-IR wavelengths is represented by a model based on Galactic source counts. The 100 mu m DIRBE observations are used as the spatial template for the interstellar medium (ISM) emission at high latitudes. Correlation of the 100 mu m data with H I column density allows us to isolate the component of the observed emission that is associated with the ISM. Limits are established on the far-IR emis sivity of the diffuse ionized medium, which indicate a lower emissivity per H nucleus than in the neutral medium. At 240 mu m, we find that adding a s econd spatial template to the ISM model can greatly improve the accuracy of the model at low latitudes. The crucial product of this analysis is a set of all-sky IR maps from which the Galactic land IPD) emission has been remo ved. We discuss systematic uncertainties and potential errors in the foregr ound subtraction process that may have an impact on studies seeking to dete ct the CIB in the residual maps.