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The Molecular ISM of Low Surface Brightness Spiral Galaxies

I summarize some results from the recent CO survey of late-type, low surface brightness (LSB) spiral galaxies by Matthews et al. (2005). We have now detected CO emission from six late-type, LSB spirals, demonstrating that despite their typical low metallicities and low mean gas surface densities, some LSB galaxies contain a molecular medium that is traced by CO. We find that the CO-detected LSB spirals adhere to the same M_H2-FIR correlation as brighter galaxies. We also find a significant drop-off in the detectability of CO among low-to-intermediate surface brightness galaxies with V_rot<~90 km/s, pointing toward fundamental changes in the physical conditions of the ISM with decreasing disk mass.