Millimeter-wavelength molecular lines and far-infrared sources

Millimeter-wavelength emission lines of HCN and CS have been detected in many galactic sources of farinfrared radiation. These sources can be divided into two classes: (I) those which do not have associated with them radio continuum emission from a compact H ir region, and (Il) those which do. An extensive map of the J = 1 0 HCN and CS emission from the W75 region suggests that molecules have comparable concentrations in the two classes of sources which may represent different stages in the formation of massive stars and star clusters. Consequences of the association of molecular sources and far-infrared sources are discussed in terms of early stellar evolution. The W75 map, and similar ones of W3, NGC 2024, and NGC 2264, show that the molecular emission is extended over much larger regions than previously realized, and consequently very large masses (> l0 -10 M0) are implied if the molecules are collisionally excited throughout the cloud. Subject headings: infrared sources - molecules, interstellar - radio lines - star formation