Halo Mass Profiles and Low Surface Brightness Galaxy Rotation Curves.

Abstract

A recent study has claimed that the rotation curve shapes and mass densities of low surface brightness (LSB) galaxies are largely consistent with ACDM predictions, in contrast to a large body of observational work. I demonstrate that the method used to derive this conclusion is incapable of distinguishing the characteristic steep CDM mass-density distribution from the core-dominated mass-density distributions found observationally: even core-dominated pseudoisothermal halos would be inferred to be consistent with CDM. This method can therefore make no definitive statements regarding the (dis)agreement between the data and CDM simulations. After introducing an additional criterion that does take the slope of the mass distribution into account, I find that only about a quarter of the LSB galaxies investigated are possibly consistent with CDM. However, for most of these, the fit parameters are so weakly constrained that this is not a strong conclusion. Of the 20 galaxies with tightly constrained fit parameters, only 3 are consistent with ACDM. Two of these galaxies are likely dominated by stars, leaving only one possible dark matter-dominated, CDM-consistent candidate. These conclusions are based on comparison of data and simulations at identical radii and fits to the entire rotation curves. LSB galaxies that are consistent with CDM simulations, if they exist, seem to be rare indeed.