Large scale structure of dust and gas in the Galaxy

Abstract

Both the large scale and intermediate scale structure of the dust and gas in the Galaxy are discussed. A set of clean all-sky maps are obtained using a physical model that describes at the four IRAS wavelengths the contaminating contribution of the zodiacal emission. Direct comparison between the 100 µm and HI column density maps shows a good correlation at high galactic latitudes. After radial unfolding the 12, 25, 60 and 100 µm radial profiles are strikingly similar and show both the molecular ring and a steep increase toward the galactic center where the 12 µm emission is relatively weak. The profiles clearly show a changing 100 µm/HI ratio which can be explained by a changing interstellar radiation field. The intermediate scale infrared structure can be separated in velocity space using high resolution HI data. There is evidence for a correlation between the HI material at anomalous velocities, with wide profiles and the corresponding dust, showing higher 60/100 µm flux ratios than the material at normal galactic velocities.