Investigating the dark matter halo of NGC 5128 using a discrete dynamical model

Context. As the nearest accessible massive early-type galaxy, NGC 5128 presents an exceptional opportunity to measure dark matter halo parameters for a representative elliptical galaxy.
Aims: Here we take advantage of rich new observational datasets of large-radius tracers to perform dynamical modeling of NGC 5128
Methods: We used a discrete axisymmetric anisotropic Jeans approach with a total tracer population of nearly 1800 planetary nebulae, globular clusters, and dwarf satellite galaxies extending to a projected distance of ∼250 kpc from the galaxy center to model the dynamics of NGC 5128.
Results: We find that a standard Navarro-Frenk-White (NFW) halo provides an excellent fit to nearly all the data, except for a subset of the planetary nebulae that appear to be out of virial equilibrium. The best-fit dark matter halo has a virial mass of M_vir = 4.4_−1.4^+2.4 × 10¹² M_⊙, and NGC 5128 appears to sit below the mean stellar mass-halo mass and globular cluster mass-halo mass relations, which both predict a halo virial mass closer to M_vir ∼ 10¹³ M_⊙. The inferred NFW virial concentration is c_vir = 5.6_−1.6^+2.4, which is nominally lower than c_vir ∼ 9 predicted from published c_vir-M_vir relations, but within the ∼30% scatter found in simulations. The best-fit dark matter halo constitutes only ∼10% of the total mass at one effective radius but ∼50% at five effective radii. The derived halo parameters are consistent within the uncertainties for models with differing tracer populations, anisotropies, and inclinations.
Conclusions: Our analysis highlights the value of comprehensive dynamical modeling of nearby galaxies and the importance of using multiple tracers to allow cross-checks for model robustness.