  We present velocity dispersion measurements of 14 globular clusters in NGC
5128 (Centarus A) obtained with the MIKE echelle spectrograph on the 6.5m
Magellan Clay telescope. These clusters are among the most luminous globular
clusters in NGC 5128 and have velocity dispersions comparable to the most
massive clusters known in the Local Group, ranging from 10 - 30 km/s. We
describe in detail our cross-correlation measurements, as well as simulations
to quantify the uncertainties. These 14 globular clusters are the brightest NGC
5128 globular clusters with surface photometry and structural parameters
measured from the Hubble Space Telescope. We have used these measurements to
derive masses and mass-to-light ratios for all of these clusters and establish
that the fundamental plane relations for globular clusters extend to an order
of magnitude higher mass than in the Local Group. The mean mass-to-light ratio
for the NGC 5128 clusters is ~3+/-1, higher than measurements for all but the
most massive Local Group clusters. These massive clusters begin to bridge the
mass gap between the most massive star clusters and the lowest-mass galaxies.
We find that the properties of NGC 5128 globular clusters overlap quite well
with the central properties of nucleated dwarf galaxies and ultracompact dwarf
galaxies. As six of these clusters also show evidence for extratidal light, we
hypothesize that at least some of these massive clusters are the nuclei of
tidally stripped dwarfs.
