OB STAR FORMATION AND H-I PRODUCTION IN MOLECULAR CLOUDS IN M33

For a sample of 38 resolved molecular clouds in M33, new H-alpha data and previously published high-resolution H I maps are analyzed to study the star formation properties of the clouds and the cycle of the gas from one phase of the interstellar medium to another. Roughly 2/3 of the molecular clouds with M > 0.5 x 10(5) M. show recent massive star formation as traced by the H-alpha emission. The high-mass star formation rates for the individual clouds range from 5 x 10(-6) to 5 x 10(-4) M. yr-1. The photodissociating flux produced by these stars is sufficient to produce the amount of atomic gas seen near the molecular clouds if the molecular clouds have a clumped structure. In addition, the relative offset of the H I and the CO peaks in the southern spiral arm is not consistent with the picture in which the atomic gas condenses in the arms to form the molecular clouds, since the H I emission appears most strongly on the downstream side of the molecular gas. The atomic hydrogen column density predicted to be associated with the mantles of molecular clouds can account for the mean H I column density seen in the inner disk of M33.