Molecular gas in the irregular galaxy NGC 4449

We present observations of the CO (J = 1-0) molecular emission in the actively star-forming irregular galaxy NGC 4449. Observations of eight positions within the optical galaxy cover a variety of H I cloud locations and levels of star-formation activity. Within a beam of 1.7 kpc we detect 1-4 x 10(7) M(.) of M(H2) in six positions, assuming conversion of CO emission to H, as appropriate for irregular galaxies and a large beam size. The size of the telescope beam, the high masses of molecular material, and the relatively high velocity dispersions observed suggest that these are molecular cloud complexes, similar to some of those found in other nearby, late-type galaxies. Except for the center of the galaxy, the molecular mass, molecular and peak H I column densities, and the ratio M(H2)/M(HI) do not vary by more than a factor of 2 between the positions. The low molecular-to-atomic gas mass ratio and high H I column densities are consistent with the molecular material being the cores of dense atomic clouds, where it is protected from UV radiation. Regions with few or no bright H II regions have molecular gas masses and gas column densities similar to those in regions containing many sites of star formation. It is not clear whether these regions will become active in the future.