The Newtonian and MOND dynamical models of NGC 5128: Investigation of the dark matter contribution

Abstract

We study the well-known nearby early-type galaxy NGC 5128 (Centaurus A) and use the sample of its globular clusters to analyze its dynamics. We study both Newtonian and MOND models assuming three cases of orbital anisotropies: isotropic case, mildly tangentially anisotropic case and the radially anisotropic case based on the literature. We find that there are two regions with different values of the velocity dispersion: interior to ~ 3 effective radii the value of the velocity dispersion is approximately 150 km s−1 , whereas beyond ~ 3 effective radii its value increases to approximately 190 km s−1 , thus implying the increase of the total cumulative mass which is indicative of the existence of dark matter there in the Newtonian approach: the mass-to-light increases from M/LB = 7 in the inner regions to M/LB = 26 in the outer regions. We found that the Navarro-Frenk-White (NFW) model with dark halo provides good description of the dynamics of NGC 5128. Using three MOND models (standard, simple and toy), we find that they all provide good fits to the velocity dispersion of NGC 5128 and that no additional dark component is needed in MOND. [Projekat Ministarstva nauke Republike Srbije, br. 176021: Visible and Invisible Matter in Nearby Galaxies: Theory and Observations]