The Global Kinematics of the Globular Cluster M92

We report the determination of high-accuracy radial velocities for 299members of the globular cluster M92 using the Hydra multi-object spectrographon the WIYN telescope. We have concentrated on stars outside of the centralregion of the cluster, located up to 14'4 from the cluster center. Candidatemembers were selected for spectroscopy based on a photometric metallicity indexdetermined from 3-band Washington photometry, also obtained with the WIYNtelescope. The median error in the velocities is 0.35 km/s. We find theheliocentric radial velocity of the cluster to be -121.2 +/-0.3 km/s. We have used an improved Bayesian analysis to determine the velocitydispersion profile of M92. The most probable profile is a cored power-law witha scale radius of 2', velocity dispersion at 1' of 6.3km/s and outer power-lawwith slope -0.6. We have also reanalyzed the M15 radial velocities of Drukieret al. (1998) and find that a pure power-law with a 1' velocity dispersion of 8km/s and slope -0.5, and the combination of a power-law with slope -0.4 andscale of 7.5 km/s inside 9' and a dispersion of 4 km/s outside, are equallylikely. In both clusters there is evidence that the samples include escapingstars. We present results from a GRAPE-based N-body simulation of an isolatedcluster that demonstrates this effect. We suggest additional tests to determinethe relative importance of tidal heating and stellar ejection for establishingthe velocity field in globular cluster halos.Comment: 55 pages, 15 figures. To appear in A