Modelling Observational Constraints for Dark Matter Halos
  Observations show that the underlying rotation curves at intermediate radii
in spiral and low-surface brightness galaxies are nearly universal. Further, in
these same galaxies, the product of the central density and the core radius
($\rho_{0}r_{0}$) is constant. An empirically motivated model for dark matter
halos which incorporates these observational constraints is presented and shown
to be in accord with the observations. A model fit to the observations of the
galaxy cluster Abell 611 shows that $\rho_{0}r_{0}$ for the dark matter halo in
this more massive structure is larger by a factor of $\sim 20$ over that
assumed for the galaxies. The model maintains the successful NFW form in the
outer regions although the well defined differences in the inner regions
suggest that modifications to the standard CDM picture are required.
