SPECTROSCOPY OF GLOBULAR-CLUSTERS IN M87 AND M49

Optical multislit spectra of globular clusters in two giant elliptical galaxies in the Virgo Cluster indicate average metal abundances of one-sixth and one-tenth solar composition for M49 and M87, respectively. These estimates are based on the strength of Mg lines. Taken together with observations of globular clusters in dwarf ellipticals this suggests a direct relation between mean metallicity of the cluster system and the luminosity of the parent galaxy which is an interesting constraint on theories of cluster formation during the protogalactic epoch. Rotation is evident in both globular cluster systems. The line-of-sight velocity dispersions of clusters in the two galaxies are estimated to be 340 ± 50 km/s (M49) and 386 ± 42 km/s (M87). Although sparsely sampled, the velocity dispersion profiles of the cluster systems are flat, suggesting the existence of an isothermal halo of dark matter in these ellipticals. A constant mass-to-light ratio can only be ruled out in the case of M87, however.