Millimeter and Submillimeter Interferometry of Astronomical Sources

The development of millimeter and submillimeter interferometers was basically motivated by the discovery, in the late 1960s and early 1970s, that trace amounts of molecular gas in the interstellar medium could be detected through millimeter-wave spectral line emission (cf Rank et al 1971). The observed lines reflected the presence of unexpectedly large amounts of molecular hydrogen, H_2 organized into giant molecular clouds where star formation takes place in the Milky Way and in other galaxies (e.g. Sanders et aI 1984). A wide variety of millimeter-wave molecular lines have also been identified in the circumstellar shells around evolved stars (cf Loup et al 1993). The intensities and Doppler shifts of these mm-wave spectral lines provide information about the density, temperature, kinematics, and chemical state of the gas. In addition, interstellar and circumstellar dust can be studied through observations of millimeter-wave continuum radiation. The success of centimeter-wavelength interferometers such as the VLA in producing fundamental new science argued that millimeter-wavelength astronomy would also benefit from the high angular resolution provided by interferometers