A search for H II regions embedded in intermediate-mass molecular clouds

The results of a radio-continuum survey of embedded H II regions of a number of relatively nearby molecular clouds of moderate size are reported. A number of flat-spectral-index sources were found, for which flux densities were measured at 1.3, 2.8, and 9 cm. The relationship of these sources with their associated molecular clouds is discussed. It is concluded that (1) the star-forming efficiency of these clouds is 2-3 percent, and possibly as high as 5 percent; (2) early-type stars can form in molecular clouds with mass more than 10,000 solar; (3) studies that predict the most massive star that can form in a molecular cloud of a given mass may be underestimating the mass of the cloud because of selection effects; and (4) an energy-balance criterion for collapse of a molecular clouds, similar to the Jeans criterion but using the turbulence kinetic energy of the cloud rather than the thermal energy, may predict where massive stars form. 34 references.