The Orbital Structure and Potential of NGC 1399

Open Access
Publisher Website
Google Scholar
Abstract
Accurate and radially extended stellar kinematic data reaching R = 97'' from the center are presented for the cD galaxy of Fornax NGC 1399. The stellar rotation is small (≤30 km s-1); the stellar velocity dispersion remains constant at 250–270 km s-1. The deviations from Gaussian line-of-sight velocity distributions are small, at the percent level. We construct dynamical models of the galaxy, deprojecting its nearly round (E0–E1) surface brightness distribution and determining the spherical distribution function that best fits (at the 4% level) the kinematic data on a grid of parameterized potentials. We find that the stellar orbital structure is moderately radial, with β = 0.3 ± 0.1 for R ≤ 60'', similar to results found for some normal giant elliptical galaxies. The gravitational potential is dominated by the luminous component out to the last data point, with a mass-to-light ratio M/LB = 10(M/L)⊙, although the presence of a central black hole of M ≈ 5 × 108 M⊙ is compatible with the data in the inner 5''. The influence of the dark component is marginally detected starting from R ≈ 60''. Using the radial velocities of the globular clusters and planetary nebulae of the galaxy, we constrain the potential more strongly, ruling out the self-consistent case and finding that the best-fit solution agrees with X-ray determinations. The resulting total mass and mass-to-light ratio are M = 1.2–2.5 × 1012 M⊙ and M/LB = 2-48(M/L)⊙ inside R = 417'' or 35 kpc for D = 17.6 Mpc.
All Related Versions

This publication has 47 references indexed in Scilit: