Globular clusters kinematics and dynamical models of the massive early-type galaxy NGC 1399

Abstract

We analyze the dynamical models of the massive early-type galaxy NGC 1399, the central galaxy of the Fornax cluster. We use the sample of 790 globular clusters as tracers of gravitational potential and we first extract the kinematics, which is then dynamically modeled. We find that the velocity dispersion remains high and approximately constant throughout the whole galaxy and that the departures from the Gaussian distribution of the orbits are not large. We use the spherical Jeans equation in both Newtonian and MOND approaches, assuming three cases of orbital anisotropies: we study isotropic, tangentially and radially anisotropic models in order to establish the best-fitting values of the mass-to-light ratios. We found that in the Newtonian approximation a significant amount of dark matter is needed and that Navarro-Frenk-White (NFW) model with a dark halo provides a satisfactory description of the kinematics of NGC 1399. We tested three MOND models (standard, simple and toy) and found that none of them can provide a fit of the velocity dispersion profile without the inclusion of dark matter. Finally, using our findings, we placed the galaxy NGC 1399 within the context of other observed early-type galaxies and discuss its location among them.