Mass density profiles of low surface brightness galaxies

We derive the mass density profiles of dark matter halos that are implied by high spatial resolution rotation curves of low surface brightness galaxies. We find that, at small radii, the mass density distribution is dominated by a nearly constant density core with a core radius of a few kiloparsecs. For rho (r) similar to r(alpha). the distribution of inner slopes at is strongly peaked around or alpha = -0.2. This is significantly shallower than the cuspy alpha less than or equal to -1 halos found in cold dark matter simulations. While the observed distribution of ct does have a tail toward such extreme values, the derived value of alpha is found to depend on the spatial resolution of the rotation curves: alpha approximate to -1 is found only for the least well resolved galaxies. Even for these galaxies, our data are also consistent with constant-density cores (alpha = 0) of modest (similar to1 kpc) core radius, which can give the illusion of steep cusps when insufficiently resolved. Consequently, there is no clear evidence for a cuspy halo in any of the low surface brightness galaxies observed.