Dynamics of the Globular Cluster System Associated with M49 (NGC 4472): Cluster Orbital Properties and the Distribution of Dark Matter

We have measured radial velocities for 196 globular clusters (GCs) aroundM49, the brightest member of the Virgo Cluster. Combined with published data,they bring the total number of GCs with measured radial velocities in thisgalaxy to 263. Using this sample, we extract the projected kinematics of thefull sample of GCs, and of the separate metal-poor and metal-rich subsamples.In agreement with previous results for the global GC kinematics based onsmaller datasets, we find that the GC system as a whole exhibits a slow overallrotation that is due almost entirely to a net rotation of the metal-poor GCsubsystem alone. In a spatial average, the metal-rich GCs shows essentially norotation. We note, however, the presence of a well defined grouping of 10metal-rich GCs that are located at opposite poles along the galaxy's major axisand which appear to be rotating at nearly 300 km/s about the minor axis. Thisgrouping may be the relic of a past merger or accretion event. Using aJeans-equation analysis, we show that the GC radial velocities alone pointunequivocally (and independently of X-ray observations) to the need for amassive dark halo associated with M49 and the Virgo B subcluster around it. Wealso show that the GC system as a whole is consistent with an almost perfectlyisotropic velocity ellipsoid. M49 is now the second elliptical galaxy (afterM87) for which we have been able to demonstrate velocity isotropy in theglobular cluster system overall, when no division based on GC color ormetallicity is attempted. Thus, the data for these two galaxies lend supportthe general assumption of isotropy when using GC kinematics to study thedark-matter distribution in early-type galaxies. (ABRIDGED)Comment: 63 pages, 21 postscript figures. Accepted for publication in the Astrophysical Journa