Dark halo properties from rotation curves

We study a large set of high spatial resolution optical rotation curves of galaxies with the goal of determining the model parameters for a disk embedded within a CDM halo that we model either with a NFW profile or pseudo-isothermal profile. We show that parameter degeneracies present in lower resolution data are lifted at these higher resolutions. 34% of the galaxies do not have a meaningful fit when using the NFW profile and 32% when using the pseudoisothermal profile, however only 14% do not have a meaningful fit in either model. In both models we find correlations between the disk baryon fraction fd and the spin parameter of the halo \', between fd and the dark halo mass M₂₀₀, and between M₂₀₀ and the concentration parameter c. We show that the distribution of the concentration parameters c, for a NFW halo, is in good agreement with CDM predictions; no significant galaxy population is found with very low values of c. The overall distribution of \' is in good agreement with theoretical predictions from hierarchical tidal torque theory. The whole sample is also well fitted by a pseudo-isothermal dark halo with a core, but the size of the core is rather small (for 70% of the sample the core size is less than 2 kpc). Thus we conclude that the profile of dark matter is steep (r^-1 or steeper) down to this radius; large dark matter cores (and therefore very low dark matter central densities) seem to be excluded. LSBs tend to have higher values of \' for a given fd and lower values of c for a given mass than HSBs. In an appendix we give some useful formula for pseudo-isothermal profile halos and discuss in detail the issue of parameter degeneracies.