In this paper , we presented metal abundance properties of 144 M81 globular clusters .
These globulars consist of the largest globular cluster sample in M81 till now .
Our main results are : the distribution of metallicities are bimodal , with metallicity peaks at { [ Fe / H ] } \approx - 1.51 and -0.58 , and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones ; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution as the metal-rich ones in M31 do ; like our Galaxy and M31 , the globular clusters in M81 have a small radial metallicity gradient .
These results are consistent with those obtained based on a small sample of M81 globular clusters .
In addition , this paper showed that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists , and that rotation is present in the metal-rich globular cluster subsample , while the metal-poor globular cluster subsample shows no evidence for rotation .
The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii .
The results of this paper confirm the conclusion of Schroder et al .
that M81 ’ s metal-rich globular clusters at intermediate projected radii were associated with a thick disk of M81 .