2001ApJ...559..828C

Surface density profiles constructed from our Washington photometry reveal the metal-poor cluster system to be more spatially extended than its metal-rich counterpart, consistent with earlier findings based on Hubble Space Telescope imaging in the central regions of the galaxy. Beyond a radius of R≃1.5R_e (10 kpc), the metal-poor component dominates the total globular cluster system.

When considered in their entirety, each of the combined, metal-poor and metal-rich globular cluster samples (278, 161, and 117 clusters, respectively) appears to rotate, with similar rotation amplitudes, about axes whose position angles are indistinguishable from that of the photometric minor axis, Θ₀=65°.

The one-dimensional rotation curve (i.e., binned in circular annuli) for the metal-rich cluster system has a roughly constant mean amplitude of ΩR=160⁺¹²⁰_–99 km.s^–1. The metal-rich clusters appear to be rotating, at all radii, about the photometric minor axis of the galaxy. However, a smoothed, two-dimensional map of the line-of-sight velocity residuals reveals the rotation field for the metal-rich clusters to be noncylindrical in nature. Instead, it exhibits a ``double-lobed'' pattern, with maxima at R∼3.5R_e-4R_e (25-30 kpc) along the approximate photometric major axis of the galaxy.

The one-dimensional rotation curve of the metal-poor cluster system has mean amplitude of ΩR=172⁺⁵¹_–108 km.s^–1. The two-dimensional map of the rotation field for the metal-poor clusters shows some evidence for solid-body rotation or, alternatively, for a ``shear'' in the line-of-sight velocity. This shear is similar in size and orientation to that observed for Virgo galaxies within 2° of M87 and is consistent with a scenario, previously suggested on the basis of dwarf galaxy kinematics and X-ray imaging, in which material is gradually infalling onto M87 along the so-called principal axis of the Virgo Cluster.

Beyond a radius of R≃2R_e (15 kpc), the approximate onset of the galaxy's cD envelope, the metal-poor globular cluster system rotates about the photometric minor axis, similar to its metal-rich counterpart. Inside this radius, however, the metal-poor clusters appear to rotate around the photometric major axis.

The complete sample of 278 globular clusters has an almost perfectly isotropic velocity ellipsoid, with β_cl=1-σ²_θ/σ²_r≃0.

When considered separately, the metal-poor cluster system shows a modest but significant tangential bias of β_cl≃-0.4, while the velocity ellipsoid of the metal-rich cluster system is radially biased, with β_cl≃0.4.