[NHM2010] 1757 , the SIMBAD biblio

We obtained spectra of 74 globular clusters (GCs) in M81. These GCs had been identified as candidates in a Hubble Space Telescope (HST) Advanced Camera for Surveys I-band survey. Sixty-eight of these 74 clusters lie within 7' of the M81 nucleus. Sixty-two 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 GCs. We combined our results with 34 M81 GC velocities and 33 metallicities from the literature and analyzed the kinematics and metallicity of the M81 GC 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 that this high mean metallicity is due to an overrepresentation of metal-rich (MR) clusters in our sample created by the spatial limits of the HST I-band survey. The metallicity distribution shows marginal evidence for bimodality, with the mean metallicities of MR and metal-poor (MP) GCs similar to those of M31 and the Milky Way. The GC system as a whole, and the MP GCs alone, show evidence of a radial metallicity gradient. The M81 GC 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 MR inner clusters. The rotation patterns among GC subpopulations are roughly similar to those of the Milky Way: clusters at small projected radii and MR clusters rotate strongly, while clusters at large projected radii and MP clusters show weaker evidence of rotation.