The Stellar and Dark Matter Halo of NGC 5128 (Centaurus A)

As the nearest large elliptical galaxy, NGC 5128 (Centaurus A) provides us with a unique opportunity to understand the stellar populations, dynamics, and halo properties of early-type galaxies. We combine complementary studies of the planetary nebulae (PNe), globular clusters (GCs), and unresolved stellar light to investigate the structure and formation of this post-merger system. We have now identified a total of 1140 PNe, and possess radial velocities for 780 PNe at distances out to 80 kpc and 50 kpc along the photometric axes. The velocity field of the PNe shows clear evidence for kinematic axis twisting, a feature predicted by models of triaxial halos and merger remnants. The mass of the dark halo continues to rise out to the limits of our survey. We also have UBVRI photometry and radial velocities for 207 GCs in NGC 5128, making this one of the largest samples of spectroscopically confirmed GCs. Our survey extends well into the halo, going out to 50 kpc and 30 kpc along the photometric axes. The metal-rich GCs are more centrally concentrated and show significant rotation about a misaligned kinematic axis, much like the PNe. The metal-poor GCs have a more extended spatial distribution and show little bulk rotation. We use these results to assess the major mechanisms proposed for the assembling of elliptical galaxies.