Spectroscopy of M81 Globular Clusters
  We obtained spectra of 74 globular clusters in M81. These globular clusters
had been identified as candidates in an HST ACS I-band survey. 68 of these 74
clusters lie within 7' of the M81 nucleus. 62 of these clusters are newly
spectroscopically confirmed, more than doubling the number of confirmed M81 GCs
from 46 to 108. We determined metallicities for our 74 observed clusters using
an empirical calibration based on Milky Way globular clusters. We combined our
results with 34 M81 globular cluster velocities and 33 metallicities from the
literature and analyzed the kinematics and metallicity of the M81 globular
cluster system. The mean of the total sample of 107 metallicities is -1.06 +/-
0.07, higher than either M31 or the Milky Way. We suspect this high mean
metallicity is due to an overrepresentation of metal-rich clusters in our
sample created by the spatial limits of the HST I-band survey. The metallicity
distribution shows marginal evidence for bimodality, with metal-rich and
metal-poor peaks approximately matching those of M31 and the Milky Way. The GC
system as a whole, and the metal-poor GCs alone, show evidence of a radial
metallicity gradient. The M81 globular cluster system as a whole shows strong
evidence of rotation, with V_r(deprojected) = 108 +/- 22 km/s overall. This
result is likely biased toward high rotational velocity due to
overrepresentation of metal-rich, inner clusters. The rotation patterns among
globular cluster subpopulations are roughly similar to those of the Milky Way:
clusters at small projected radii and metal-rich clusters rotate strongly,
while clusters at large projected radii and metal-poor clusters show weaker
evidence of rotation.
