Metal Abundance Properties of M81 Globular Cluster System

This paper is the third in a series of papers on M81 globular clusters. In this paper, we present spatial and metal abundance properties of 95 M81 globular clusters, which comprise nearly half the entire M81 globular cluster system. These globular clusters are divided into two M81 metallicity groups by a KMM test. Our results show that the metal-rich clusters did not demonstrate a centrally concentrated spatial distribution the way the clusters in M31 do, and metal-poor clusters tend to be less spatially concentrated. In other words, the distribution of the metal-rich clusters in M81 is not very similar to that of M31. The quick histogram shows that most of the metal-rich clusters are distributed at projected radii of 4-8 kpc. Note also that the metal-rich clusters are distributed within the inner 20 kpc, and the metal-poor ones, out to radii of ?40 kpc. Like our Galaxy and M31, the metallicity distribution of globular clusters in M81 along a galactocentric radius suggests that some dissipation occurred during the formation of the globular cluster system; i.e., smooth, pressure-supported collapse models of galaxies are unlikely to produce the type of radial distribution of metallicity presented in this paper. There is no evident correlation between globular cluster luminosity and metallicity in M81 globular clusters. The overwhelming conclusion of this paper seems to be that a more complete and thorough cluster search is needed in M81.