A model of the far-infrared emission from the Galaxy

The warm dust (< 25 K) that lies in the plane of the Galaxy (scaleheight of about 0.13 kpc) was detected by IRAS and is preferentially associated with star formation regions. In this paper we describe a model of the !diffuse far-infared emission from cool dust within the Galaxy. We identify a more diffuse, cool (18-22 K) dust component (scaleheight of about 0.5 kpc) that has been detected by the DIRBE (at 140 and 240 mu m) on the COBE satellite. This dust may be supported above the Galactic plane by radiation pressure. We show that the excess emission cannot be accounted for by the far-infrared background (upper limits of 1.0 and 0.5 MJ sr(-1) at 140 and 240 mu m respectively) or by the zodiacal light. The total luminosity of this cool component is approximate to 7 x 10(9) L., and it has a mass of approximate to 3 x 10(7) M.. We calculate extinction values for the cool component of A(upsilon) approximate to 27 mag towards the Galactic Centre, and A(upsilon) approximate to 0.3 mag at the poles.