Photometric studies of globular clusters in the Andromeda nebula. III. Metallicity gradient of the subsystem of globular clusters in M 31.

A definite correlation is found between the apparent galactocentric distance of the globular clusters in M31 and their metallicity parameters, based on a series of photometric observations. At a distance of 10 kpc the radial gradient of the metal abundance for the forbidden line of Fe/H is determined to be around -0.15 per kpc. At larger distances the clusters tend to have a lower but constant metallicity. The presence of a metallicity gradient for the globular cluster subsystems in the Galaxy and in M31 suggests that the two galaxies experienced a similar history of element-heavy-element enrichment during their initial evolution. A graph is presented which describes the variations in the metallicity parameters of the globular clusters in M31 with their apparent distance from the galactic center.