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

We present a dynamical analysis of the globular cluster system associated w ith M87 (=NGC 4486), the cD galaxy near the dynamical center of the Virgo C luster. The analysis utilizes a new spectroscopic and photometric database, which is described in a companion paper. Using a sample of 278 globular cl usters with measured radial velocities and metallicities and new surface de nsity profiles based on wide-field Washington photometry, we study the dyna mics of the M87 globular cluster system both globally (for the entire clust er sample) and separately (for the metal-rich and metal-poor globular clust er samples). This constitutes the largest sample of radial velocities for p ure Population II tracers yet assembled for any external galaxy. Our princi pal findings are summarized as follows : 1. Surface density profiles constructed from our Washington photometry reve al the metal-poor cluster system to be more spatially extended than its met al-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, respective ly) appears to rotate, with similar rotation amplitudes, about axes whose p osition angles are indistinguishable from that of the photometric minor axi s, 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 Ome gaR = 160(-99)(+120) km s(-1). The metal-rich clusters appear to be rotatin g, at all radii, about the photometric minor axis of the galaxy. However, a smoothed, two-dimensional map of the line-of-sight velocity residuals reve als the rotation field for the metal-rich clusters to be noncylindrical in nature. Instead, it exhibits a "double-lobed" pattern, with maxima at R sim ilar to 3.5R(e)-4R(e) (25-30 kpc) along the approximate photometric major a xis 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 v elocity. 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 imag ing, 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 counter part. 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 iso tropic 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, whi le the velocity ellipsoid of the metal-rich cluster system is radially bias ed, with beta (cl) similar or equal to 0.4. Taken together, these results demonstrate that the dual nature of the M87 g lobular cluster system, first identified on the basis of its bimodal metall icity distribution, also extends to its dynamical properties. We discuss th e implications of these findings for the various formation scenarios propos ed for giant elliptical galaxies and their globular cluster systems.