The Metallicity of Globular Cluster Systems

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Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[74.15] The Metallicity of Globular Cluster Systems

Keith M. Ashman, Christina M. Bird (U.\ Kansas)

There is increasing evidence that globular cluster systems around many galaxies are comprised of two or more distinct populations. This idea is well-established for the Milky Way, where the globular cluster system can be separated into disk and halo components. More recent analyses of the metallicity distributions of globular cluster systems around nearby galaxies suggest that these systems are also comprised of two or more components. We suggest that the metal-poor subsystems contain the only genuine ``first generation" globulars, with secondary events such as galaxy mergers being responsible for more metal-rich globular clusters. We show that current data are consistent with a universal mean metallicity for such first generation globular cluster systems. The observation that the metallicity of globular cluster systems increases with galaxy luminosity appears to be a result of bright galaxies having a higher fraction of metal-rich clusters (possibly because a larger proportion of their globulars formed in merging events). On the basis of these results, we argue that first generation globulars form within protogalaxies from primordial material, with self-enrichment producing their observed metal content.

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