The Dynamics of the M87 Globular Cluster System

We present the results from a study of the dynamics of the system of globularclusters around M87. After eliminating foreground galactic stars and backgroundgalaxies, we end up with a sample of 205 bona fide M87 globular clusters forwhich we have radial velocities determined from multi-slit spectra taken withthe LRIS on the Keck Telescope. We find that the mean radial velocity of theM87 globular clusters agrees well with that of M87 itself, and that thevelocity histogram is well represented by a Gaussian distribution. We findevidence for rotation in the globular cluster system. We find that the observedvelocity dispersion of the M87 globular cluster system increases with radiusfrom 270 \kms~ at $r$ = 9 kpc to $\approx$400 \kms~ at $r$ = 40 kpc. Theinferred mass-to-light ratio in solar units increases from 5 at $r$ = 9 kpc to$\approx$30 at $r$ = 40 kpc with $M(r) \sim r^{1.7}$. The long slit opticalspectroscopy near the center of M87 and the recent analysis of the ROSAT X-raydata are in good agreement with this analysis near the nucleus and in the outerparts of M87 respectively.Comment: 29 pages, TeX, with 6 Figures. Accepted for publication in the Ap