Mass density profiles of low surface brightness galaxies

We derive the mass density profiles of dark matter halos that are implied b y high spatial resolution rotation curves of low surface brightness galaxie s. 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 st rongly 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 si mulations. While the observed distribution of ct does have a tail toward su ch extreme values, the derived value of alpha is found to depend on the spa tial resolution of the rotation curves: alpha approximate to -1 is found on ly for the least well resolved galaxies. Even for these galaxies, our data are also consistent with constant-density cores (alpha = 0) of modest (simi lar to1 kpc) core radius, which can give the illusion of steep cusps when i nsufficiently resolved. Consequently, there is no clear evidence for a cusp y halo in any of the low surface brightness galaxies observed.