Using NMAGIC to probe the dark matter halo and orbital structure of the
  X-ray bright, massive elliptical galaxy, NGC 4649
  We create dynamical models of the massive elliptical galaxy, NGC 4649, using
the N-body made-to-measure code, NMAGIC, and kinematic constraints from
long-slit and planetary nebula (PN) data. We explore a range of potentials
based on previous determinations from X-ray observations and a dynamical model
fitting globular cluster (GC) velocities and a stellar density profile. The
X-ray mass distributions are similar in the central region but have varying
outer slopes, while the GC mass profile is higher in the central region and on
the upper end of the range further out. Our models cannot differentiate between
the potentials in the central region, and therefore if non-thermal pressures or
multi-phase components are present in the hot gas, they must be smaller than
previously inferred. In the halo, we find that the PN velocities are sensitive
tracers of the mass, preferring a less massive halo than that derived from the
GC mass profile, but similar to one of the mass distributions derived from
X-rays. Our results show that the GCs may form a dynamically distinct system,
and that the properties of the hot gas derived from X-rays in the outer halo
have considerable uncertainties that need to be better understood. Estimating
the mass in stars using photometric information and a stellar population
mass-to-light ratio, we infer a dark matter mass fraction in NGC 4649 of ~0.39
at 1Re (10.5 kpc) and ~0.78 at 4Re. We find that the stellar orbits are
isotropic to mildly radial in the central ~6 kpc depending on the potential
assumed. Further out, the orbital structure becomes slightly more radial along
R and more isotropic along z, regardless of the potential assumed. In the
equatorial plane, azimuthal velocity dispersions dominate over meridional
velocity dispersions, implying that meridional velocity anisotropy is the
mechanism for flattening the stellar system.
