New CO data from the high-resolution Massachusetts-Stony Brook survey are analyzed to understand the mechanisms responsible for high-mass OB star formation. For a sample of 94 giant molecular clouds associated with high-luminosity radio H II regions, the efficiency (per unit mass of H2) for OB star formation decreases significantly with increasing cloud mass over the range 105 to 3×106M_sun;. It is concluded therefore that massive star formation is generally not stimulated by an internal mechanism such as expanding H II regions in sequential star formation models, which should have a higher efficiency in larger clouds. Instead, it is proposed that OB stars form as a result of cloud-cloud collisions. Cloud-cloud collisions could also account for high rates of massive star formation in the nuclei of high-luminosity infrared galaxies.
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Scoville et al. (1986) studied this question.