The authors have obtained spectra and radial velocities for 26 globular cluster candidates surrounding M87. Almost all of the brighter objects are either foreground stars or members of a background cluster of galaxies at a redshift of ≡0.09. Nearly all of the objects that the authors observed that are fainter than 20.5 in B are bona fide globular clusters. They have determined radial velocities for ten of these. Their mean projected distance from M87 is 3.9 arcmin, corresponding to 18.0 kpc at an assumed distance of 15.7 Mpc. Their velocity dispersion is 440 km s⁻¹, and the integrated mass of M87 derived by the projected-mass method is 6.1×10¹²M_sun;. This result falls very close to the M ≡ r line that connects the mass measures for the inner regions of M87 derived from the galaxy's own velocity dispersion versus radius relation and the outer X-ray halo determinations. The blue mass-to-light ratio inside this radius is ≡150 in solar units.
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Huchra et al. (1987) studied this question.