  We present rotation curves of 19 galaxies from THINGS, The HI Nearby Galaxy
Survey. The high spatial and velocity resolution of THINGS make these the
highest quality HI rotation curves available to date for a large sample of
nearby galaxies, spanning a wide range of HI masses and luminosities. The high
quality of the data allows us to derive the geometrical and dynamical
parameters using HI data alone. We do not find any declining rotation curves
unambiguously associated with a cut-off in the mass distribution out to the
last measured point. The rotation curves are combined with 3.6 um data from
SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models. Our
best-fit, dynamical disk masses, derived from the rotation curves, are in good
agreement with photometric disk masses derived from the 3.6 um images in
combination with stellar population synthesis arguments and two different
assumptions for the stellar Initial Mass Function (IMF). We test the Cold Dark
Matter-motivated cusp model, and the observationally motivated central density
core model and find that (independent of IMF) for massive, disk-dominated
galaxies, all halo models fit apparently equally well; for low-mass galaxies,
however, a core-dominated halo is clearly preferred over a cuspy halo. The
empirically derived densities of the dark matter halos of the late-type
galaxies in our sample are half of what is predicted by CDM simulations, again
independent of the assumed IMF.
