THE MOLECULAR-HYDROGEN CONTENT OF NGC-604 AND OTHER M33 H-II REGION COMPLEXES

We have searched six bright H II regions in M33 for H2 line emission. Previously detected fluorescent H2 emission in the first-ranked M33 H II region, NGC 604, has been mapped, allowing us to estimate the mass of its molecular cloud (of order 3 x 106Mo). This result implies a ratio Ico/N(H2) lower by an order of magnitude than that of galactic molecular clouds. The lack of shocked H2 in NGC 604 implies that the ionized stellar wind bubbles seen in the nebula are not interacting strongly with the molecular material. The dynamics of NGC 604 appear to be dominated by gravitational interaction. A 2-μm spectrum of NGC 604 also shows H I and He I recombination lines from the ionized gas, as well as CO absorption in the photospheres of late-type stars, which must dominate the 2-μm continuum. With the exception of IC 133, the other H II regions yielded only upper limits for H2 emission. IC 133 appears to contain an unusually small amount of gas and dust. The lack of H2 in the other regions is briefly discussed. © 1990 Oxford University Press. All rights reserved.