Submillimeter Wave Astronomy

Scientific Overview Astronomical observations at submillimeter wavelengths, between 40 μm and 1 mm, study astro-physical sources and problems which differ from and complement those accessible at other wavelengths. Although a few nonthermal sources are known, most of the radiation observed in this spectral band from astronomical sources outside of the solar system comes from extended clouds of gas and dust with temperatures in the range 10-500 K and densities between 10 and 10 6 atoms cm −3 . The submillimeter radiation consists of both continuous emission from the sub-micron sized dust particles, which make up ∼ 1% of the total mass, and line emission from atomic and molecular species in the gas. The energy radiated at submillimeter wavelengths is generally supplied to such a cloud in the form of ultraviolet, optical, or near infrared radiation from stars or other luminous objects which is absorbed by the dust and goes into heating the dust and gas. Since only a small amount of dust is required to convert ultraviolet and optical radiation into submillimeter radiation, there are many astronomical sources from which most or all of the observed energy lies in this spectral region, although the objects which heat the dust and gas differ from one submillimeter source to another. Thus intense submillimeter radiation is seen from the center of our Galaxy 1 and from diffusely distributed matter within the galactic plane 2, where the heating is probably due to normal stars; from the nuclei of several other galaxies 3, where exotic heating sources may be important; and from shells of dust and gas which are expelled from and heated by evolving stars 4.