The M31 globular cluster system

One hundred and nine new globular cluster candidates around M31 have been identified on the Canada-France-Hawaii telescope (CFHT) prime-focus slitless spectra plates. All previously recognized clusters (Sargent, et al., 1977; Vetesnick, 1962; and Battistini et al., 1980) were examined on the plates, and a compilation made of 509 objects which have the appearance and spectra of globular clusters. Of these objects, 408 have colors typical of globular clusters in the Galaxy. Methods were devised to estimate the core radii and intrinsic colors of most of the 509 clusters. The characteristics of the globular cluster systems of M31 and the Galaxy are very similar. In particular, the radial frequency distributions and the core radii distributions of the two systems are virtually identical. The mean luminosity of globular clusters decreases significantly with increasing galactocentric distance; the clusters with projected distances from the nucleus greater than 10 kpc are, in the mean, 0.7 mag fainter than those closer to the center. There is no evidence of a radial color gradient in the data, which extend, however, to only about 25 kpc, mainly along the major axis.