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

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: antoine.dumont.neira@gmail.com
² Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City UT 84112, USA
³ Department of Physics and Astronomy Michigan State University Biomedical & Physical Sciences, 567 Wilson Rd, Room 3275 East Lansing, MI 48824-2320 Michigan, USA
⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁵ Universite de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁶ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁷ University of Tampa, 401 West Kennedy Boulevard, Tampa, FL 33606, USA
⁸ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
⁹ Department of Astronomy, University of Michigan, Ann, Arbor, MI 48109, USA
¹⁰ Center for Cosmology and Particle Physics, Department of Physics, New York University, 726 Broadway, New York, NY 10003, USA

Received: 20 June 2023
Accepted: 21 February 2024

Abstract

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.