Mapping the dark matter halo of early-type galaxy NGC 2974 through
  orbit-based models with combined stellar and cold gas kinematics
  We present an orbit-based method of combining stellar and cold gas kinematics
to constrain the dark matter profile of early-type galaxies. We apply this
method to early-type galaxy NGC 2974, using Pan-STARRS imaging and SAURON
stellar kinematics to model the stellar orbits, and introducing HI kinematics
from VLA observation as a tracer of the gravitational potential. The
introduction of the cold gas kinematics shows a significant effect on the
confidence limits of especially the dark halo properties: we exclude more than
$95\%$ of models within the $1-\sigma$ confidence level of Schwarzschild
modelling with only stellar kinematics, and reduce the relative uncertainty of
the dark matter fraction significantly to $10\%$ within $5 R_\mathrm{e}$.
Adopting a generalized-NFW dark matter profile, we measure a shallow cuspy
inner slope of $0.6^{+0.2}_{-0.3}$ when including the cold gas kinematics in
our model. We cannot constrain the inner slope with the stellar kinematics
alone.
