The dust/gas correlation at high Galactic latitude

We have correlated the far-infrared emission from dust as measured by the DIRBE and FIRAS experiments with the 21-cm emission from gas as measured by the Leiden/Dwingeloo survey of HI in our Galaxy. A tight correlation is observed at high [b] at wavelengths ranging from 100 mu m to 1 mm. The dust emission spectrum derived from the correlation is fit well by a single Planck curve characterized by T = 17.5 K and an emissivity proportional to nu(2). The dust emissivity tau/N-H = 1.0 10(-25) (lambda/250 mu m)(-2) cm(2) is remarkably close to the value in the Draine and Lee (1984) dust model and is much smaller than values predicted Eor porous or fractal grains. In the emission from HI gas, we exclude the presence of a very cold dust component with comparable emissivity, unless its temperature is significantly smaller than 7 K. We also discuss the contribution from Galactic molecular and ionized gas to the global IR emission.