Comparing X-ray and Dynamical Mass Profiles in the Early-Type Galaxy NGC
  4636
  We present the results of an X-ray mass analysis of the early-type galaxy NGC
4636, using Chandra data. We have compared the X-ray mass density profile with
that derived from a dynamical analysis of the system's globular clusters (GCs).
Given the observed interaction between the central active galactic nucleus and
the X-ray emitting gas in NGC 4636, we would expect to see a discrepancy in the
masses recovered by the two methods. Such a discrepancy exists within the
central ~10kpc, which we interpret as the result of non-thermal pressure
support or a local inflow. However, over the radial range ~10-30kpc, the mass
profiles agree within the 1-sigma errors, indicating that even in this highly
disturbed system, agreement can be sought at an acceptable level of
significance over intermediate radii, with both methods also indicating the
need for a dark matter halo. However, at radii larger than 30kpc, the X-ray
mass exceeds the dynamical mass, by a factor of 4-5 at the largest
disagreement. A Fully Bayesian Significance Test finds no statistical reason to
reject our assumption of velocity isotropy, and an analysis of X-ray mass
profiles in different directions from the galaxy centre suggests that local
disturbances at large radius are not the cause of the discrepancy. We instead
attribute the discrepancy to the paucity of GC kinematics at large radius,
coupled with not knowing the overall state of the gas at the radius where we
are reaching the group regime (>30kpc), or a combination of the two.
