Star Clusters in M31: V. Internal Dynamical Trends: Some Troublesome,
  Some Reassuring
  We present internal velocity dispersions and precise radial velocities for
200 globular clusters (GCs) in M31 that are derived using new high-resolution
spectra from MMT/Hectochelle. Of these, 163 also have King model structural
parameters that allow us to estimate their mass-to-light ratios. This is, by
far, the largest such dataset available for any galaxy, including the Milky
Way. These data strongly confirm earlier suggestions that the optical and
near-infrared mass-to-light ratios of M31 GCs decline with increasing
metallicity. This behavior is the opposite of that predicted by stellar
population models for a standard initial mass function. We show that this
phenomenon does not appear to be caused by standard dynamical evolution. A
shallower mass function for metal-rich GCs (with dN/dM ~ M^-0.8 to M^-1.3 below
one solar mass) can explain the bulk of extant observations. We also observe a
consistent, monotonic correlation between mass-to-light ratio and cluster mass.
This correlation, in contrast to the correlation with metallicity, is
well-explained by the accepted model of dynamical evolution of GCs through mass
segregation and the preferential loss of low-mass stars, and these data are
among the best available to constrain this process.
