Improved Modeling of the Mass Distribution of Disk Galaxies by the
  Einasto Halo Model
  (Abridged) The analysis of the rotation curves (RCs) of spiral galaxies
provides an efficient diagnostic for studying the properties of dark matter
halos and their relations with the baryonic material. We have modeled the RCs
of galaxies from The HI Nearby Galaxy Survey (THINGS) with the Einasto halo
model, which has emerged as the best-fitting model of the halos arising in
dissipationless cosmological N-body simulations. We find that the RCs are
significantly better fit with the Einasto halo than with either a
pseudo-isothermal sphere (Iso) or Navarro-Frenk-White (NFW) halo models. In our
best-fit models, the radius of density slope -2 and the density at this radius
are highly correlated. The Einasto index, which controls the overall shape of
the density profile, is near unity on average for intermediate and low mass
halos. This is not in agreement with the predictions from LCDM simulations. The
indices of the most massive halos are in rough agreement with those of
cosmological simulations and appear correlated with the halo virial mass. We
find that a typical Einasto density profile declines more strongly in its
outermost parts than any of the Iso or NFW models whereas it is relatively
shallow in its innermost regions. The core nature of those regions of halos
thus extends the cusp-core controversy found for the NFW model with low surface
density galaxies to the Einasto halo with more massive galaxies like those of
THINGS. We thus find that the Einasto halo model provides, so far, the best
match to the observed RCs, and can therefore be considered as a new standard
model for dark matter halos.
