The Molecular ISM in Low Surface Brightness Disk Galaxies

We present models for the interstellar medium in disk galaxies. Inparticular, we investigate whether the ISM in low surface brightness galaxiescan support a significant fraction of molecular gas given their low metallicityand surface density. It is found that the abundance and line brightness of COin LSB galaxies is small and typically below current observational limits.Still, depending on physical details of the ISM, the fraction of gas in theform of molecular hydrogen can be significant in the inner few kpc of a lowsurface brightness galaxy. This molecular gas would be at temperatures of$\sim$ 30 -- 50 K, rather higher than in high surface brightness galaxies.These results may help explain the star forming properties and inferredevolutionary history of LSB galaxies.