The Navarro-Frenk-White profile (NFW profile) is a spatial mass distribution function (not "mass function" in the sense of a PMF) for the internals of dark matter halos, developed from cosmological N-body simulations run by Navarro, Frenk, and White. The distribution has been adopted for use within other models.
ρ0 ρ(r) = ————————————— r/Rs(1+r/Rs)2
The latter two (parameters) must be chosen to fit the halo. Generalized NFW profiles (GNFW profiles) generalize this model: example using a form attributed to Zhao (Zhao profile):
ρ0 ρ(r) = —————————————————— (r/Rs)β(1+r/Rs)3-β