2.6. Metallicities

The presence of compact clusters appears to be uncorrelated with the metallicity of the environment; this is an important factor that should be considered in models attempting to account for the formation of these objects. A number of clusters are present in the dwarf galaxy I Zw 18 (Meurer et al. 1995); with a gas-phase oxygen abundance of 1/50 that of the Sun (Dufour, Garnett, & Shields 1988), it is the most metal-deficient galaxy known. The brightest cluster in NGC 1275, on the other hand, evidently has a metallicity roughly close to solar (Zepf et al. 1995), as might be expected considering that the host is a cD galaxy. Finally, circumnuclear rings (Section 4), which occur almost exclusively in early-type spirals (e.g., Ho, Filippenko, & Sargent 1996a), are well known to have high metal abundances, often exceeding solar (e.g., Storchi-Bergmann, Wilson, & Baldwin 1996).