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Globular Clusters as Dynamical Probes of the
Virgo Giant Elliptical M49
T.J. Bridges et al.
Anglo-Australian Observatory, Australia
We have obtained spectra and velocities for 144 globular clusters
in the Virgo giant elliptical M49, and are using these data to study
the kinematics, ages and abundances of the globular clusters, and
the dynamics, dark matter content, and origin of M49. The metal-
poor clusters have signicantly higher velocity dispersion than the
metal-rich clusters. We also nd little or no rotation in the more
spatially concentrated metal-rich population, with a resulting 3
upper limit of v/ < 0.4 for this population. We conrm X-ray
evidence for a dark matter halo in M49, nding a M/LB  70
at 50 kpc galactocentric radius. We derive ages and metallicities
from binned spectra of 131 clusters, and nd that the clusters
span a metallicity range of 1.6  [Fe/H]  0. Within the errors
the clusters are old and coeval, with t > 6 Gyr at 95% condence.
Though not formally signicant, the metal-rich population is 
0.7 Gyr younger than the metal-poor population. Our results are
most consistent with a merger origin for M49, with the formation
of a second generation of younger, more metal-rich clusters during
the merger.
Co-authors: K. Ashman, M. Beasley, D. Geisler, D. Hanes, R.
Sharples, S. Zepf
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