NGC 5128 as an isotropic rotator

NGC 5128 is a well-studied elliptical galaxy with an excellent kinematic data set for planetary nebulae that has been modeled up until now only by solving the Jeans equation for spherical systems. As a first approximation beyond spherical symmetry, we model the galaxy as an axisymmetric system flattened by rotation with isotropic velocity distribution. We propose a new version of such an isotropic rotator having a cuspy density profile with NFW-like behavior. The solutions of the Jeans equations for a single component of such form do not reproduce the data well: the rotation curve rises too slowly with radius, and the velocity dispersion profile drops too fast. The data are well fitted, however, by a system built with two components: a more compact, flattened, less massive, fast-rotating and cold bulge and an extended, almost spherical, more massive, slow-rotating, and hot halo. This picture agrees well with the results of recent N-body simulations of galaxy mergers, which tend to produce oblate rotating spheroids. The total mass of the system is estimated to be (9.1 +/- 3.5) x 10(11) solar masses, and the mass-to-light ratio is only 26 +/- 17 solar units.