Extragalactic globular clusters. III - Metallicity comparisons and anomalies

Abstract

Using a method based on the strengths of six absorption line indices measured in integrated spectra, we have derived metallicities for 22 globular clusters associated with the Sc galaxy, M33, 10 globular clusters associated with the giant elliptical galaxy, M87, eight globular clusters associated with the Sb(r)I-II galaxy, M81, and three globular clusters associated with the Fornax dwarf elliptical galaxy. In addition, we have derived mean metallicities for 38 bright galaxies, mostly ellipticals, 29 dwarf elliptical galaxies in the Virgo cluster, 10 dwarf elliptical galaxies in the Fornax cluster and four local group dwarf galaxies. Comparing these results with metallicities we previously derived for 149 clusters in M31 and with the Milky Way cluster metallicities, we show that the mean metallicity of a cluster system is linearly related to the luminosity of the parent galaxy. A similar relationship is suggested between galaxy metallicity and luminosity for the bright and dwarf galaxies, although metallicity is not the only parameter differentiating the spectroscopic properties of galaxies. The slope of the relationshIp between the mean metallicity of a cluster system and parent galaxy luminosity is very similar to the slope of the relationship between galaxy metallicity and luminosity, but there is an offset in the sense that the clusters are more metal poor. Investigation of the distribution of 12 different line strength indices versus metallicity for clusters and galaxies shows a remarkable uniformity in abundance characteristics among these diverse populations. The only apparent abundance anomalies are in the strengths of cyanogen (4170 A) and the Ca II H and K lines, both of which are enhanced in M31 globular clusters