Dynamics of the globular cluster system associated with M87 (NGC 4486).: II.: Analysis

We present a dynamical analysis of the globular cluster system associated with M87 (=NGC 4486), the cD galaxy near the dynamical center of the Virgo Cluster. The analysis utilizes a new spectroscopic and photometric database, which is described in a companion paper. Using a sample of 278 globular clusters with measured radial velocities and metallicities and new surface density profiles based on wide-field Washington photometry, we study the dynamics of the M87 globular cluster system both globally (for the entire cluster sample) and separately (for the metal-rich and metal-poor globular cluster samples). This constitutes the largest sample of radial velocities for pure Population II tracers yet assembled for any external galaxy. Our principal findings are summarized as follows : 1. 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 similar or equal to 1.5R(e) (10 kpc), the metal-poor component dominates the total globular cluster system. 2. 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, Theta (0) = 65 degrees. 3. The one-dimensional rotation curve (i.e., binned in circular annuli) for the metal-rich cluster system has a roughly constant mean amplitude of OmegaR = 160(-99)(+120) 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 similar to 3.5R(e)-4R(e) (25-30 kpc) along the approximate photometric major axis of the galaxy. 4. The one-dimensional rotation curve of the metal-poor cluster system has mean amplitude of OmegaR = 172(-108)(+51) 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 degrees 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. 5. Beyond a radius of R similar or equal to 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. 6. The complete sample of 278 globular clusters has an almost perfectly isotropic velocity ellipsoid, with beta (cl) = 1 - sigma (2)(theta)/sigma (2)(r) similar or equal to 0. 7. When considered separately, the metal-poor cluster system shows a modest but significant tangential bias of beta (cl) similar or equal to -0.4, while the velocity ellipsoid of the metal-rich cluster system is radially biased, with beta (cl) similar or equal to 0.4. Taken together, these results demonstrate that the dual nature of the M87 globular cluster system, first identified on the basis of its bimodal metallicity distribution, also extends to its dynamical properties. We discuss the implications of these findings for the various formation scenarios proposed for giant elliptical galaxies and their globular cluster systems.