AND ASTROPHYSICS Correlation properties of the diffuse light from COBE-FIRAS maps

Abstract. Wesearch for a cosmic component of the far-infrared and submillimetre background using the data from the COBE-FIRAS instrument. From the correlation properties of the diffuse light maps obtained after all the foregrounds and discrete source contributions have been removed, we claim that the rms bright-ness is given by (I)rms ’ 4 (=400m)−3:1nWm−2sr−1 for 400m. At angular scales ranging from few degrees to few tens of degrees we find a steepening of the angular auto-correlation function with respect to the behaviour derived from galaxy surveys at smaller angular scales, becaming its spectral index γ 2, in agreement with the indications inferred from galaxy catalogues at similar scales. In addition it is found that the genus distributions of the diffuse light maps are consistent with a random gaussian field with a coherence angle 5:9, in agreement with COBE-DMR. These evidences support the extragalactic origin of the detected residual far-infrared back-ground. Key words: cosmic microwave background – large-scale-structure of Universe – diffuse radiation – infrared: galaxies 1