The distribution of the ISM in the Milky Way

We use the COBE/DIRBE (1.2, 2.2, 60, 100, 140 and 240 mu m) maps and the COBE/FIRAS spectra (for the wavelength range 100 - 1000 mu m) to constrain a model for the spatial distribution of the dust, the stars and the gas in the Milky Way. By assumming exponential axisymmetric distributions for the dust and the stars and by performing the corresponding radiative transfer calculations we reproduce the FIR and NIR maps of the Milky Way. Similar distributions for the atomic and molecular hydrogen in the disk are used (with an inner cut off radius for the atomic Hydrogen) to fit the gas data. The star formation rate surface density is ploted against the gas surface density and an "intrinsic" Galactic Schmidt law is derived with excellent agreement with the "external" Schmidt law found for spiral galaxies. The Milky Way is found to consume similar to 1% and similar to 10% of its gas in the outer and inner regions respectively (for a period of 0.1 Gyr) for making stars. The dust-induced B-V colour excess observed in various directions and distances (up to similar to 6.5 kpc) to well studied Cepheid stars is compared with the model predictions showing a good agreement. The simple assumption of exponential distributions of stars and dust in the Galaxy is found to be quite instructive and adequate in modelling all the available data sets from 0.45 mu m (B-band) to 1000 mu m.