The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters

We study the kinematics and dynamics of the globular cluster system of NGC1399, the central galaxy of the Fornax cluster. The observational data consistsof medium resolution spectra, obtained at the Very Large Telescope. Our samplecomprises 468 radial velocities in the magnitude range 20 < m_R < 23. This isthe largest sample of globular cluster velocities around any galaxy obtained sofar. The radial range is 2 arcmin < r < 9 arcmin, corresponding to 11 kpc to 50kpc of galactocentric distance. There is the possibility that unbound clustersand/or objects in the foreground contaminate the NGC 1399 cluster sample. Understrong error selection, practically no objects are found with velocities lowerthan 800 km/s or higher than 2000 km/s. Since the extreme velocities influencethe velocity dispersion considerably, uncertainty regarding the exact value ofthe dispersion remains. Within the above velocity limits, we derive a projectedvelocity dispersion for the total sample of 274+-9 km/s which within theuncertainties remains constant over the entire radial range. Without anyvelocity restriction, it increases to 325 km/s. Blue and red clusters showdifferent dispersions corresponding to their different surface densityprofiles. Spherical models point to a circular velocity of 415+-30$ km/s,assuming isotropy for the red clusters. This value is constant out to 40 kpc.The inferred dark halo potential can be well represented by a logarithmicpotential. Also a halo of the NFW type fits well to the observations. Some massprofiles derived from X-ray analyses do not agree with a constant circularvelocity within our radial range, irrespective of its exact value.Comment: 38 pages, 20 figures, accepted by A