High-resolution rotation curves of low surface brightness galaxies. II. Mass models

We present mass models for a sample of 30 high-resolution rotation curves of low surface brightness galaxies. We fit both pseudoisothermal (core dominated) and cold dark matter (CDM; cusp dominated) halos for a wide variety of assumptions about the stellar mass-to-light ratio. We find that the pseudoisothermal model provides superior fits. CDM fits show systematic deviations from the data and often have a small statistical likelihood of being the appropriate model. The distribution of concentration parameters is too broad, and has too low a mean, to be explained by low-density, flat CDM (Lambda CDM). This failing becomes more severe as increasing allowance is made for stellar mass: Navarro, Frenk, & White (NFW) model fits require uncomfortably low mass-to-light ratios. In contrast, the maximum disk procedure does often succeed in predicting the inner shape of the rotation curves, but it requires uncomfortably large stellar mass-to-light ratios. The data do admit reasonable stellar population mass-to-light ratios if halos have cores rather than cusps.