The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: III. Separation of Galactic Emission from the Infrared Sky Brightness

摘要

The Cosmic Infrared Background (CIB) is hidden behind veils of foregroundemission from our own solar system and Galaxy. This paper describes proceduresfor removing the Galactic IR emission from the 1.25 - 240 micron COBE DIRBEmaps as steps toward the ultimate goal of detecting the CIB. The Galacticemission models are carefully chosen and constructed so that the isotropic CIBis completely retained in the residual sky maps. We start with DIRBE data fromwhich the scattered light and thermal emission of the interplanetary dust (IPD)cloud have already been removed. Locations affected by the emission from brightcompact and stellar sources are excluded from the analysis. The unresolvedemission of faint stars at near- and mid-IR wavelengths is represented by amodel based on Galactic source counts. The 100 micron DIRBE observations areused as the spatial template for the interstellar medium (ISM) emission at highlatitudes. Correlation of the 100 micron data with H I column density allows usto isolate the component of the observed emission that is associated with theISM. Limits are established on the far-IR emissivity of the diffuse ionizedmedium, which indicate a lower emissivity per H nucleus than in the neutralmedium. At 240 micron, we find that adding a second spatial template to the ISMmodel can greatly improve the accuracy of the model at low latitudes. Thecrucial product of this analysis is a set of all-sky IR maps from which theGalactic (and IPD) emission has been removed. We discuss systematicuncertainties and potential errors in the foreground subtraction process thatmay have an impact on studies seeking to detect the CIB in the residual maps.