The Globular Cluster Systems of Elliptical Galaxies

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Session 52 -- Elliptical Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[52.02] The Globular Cluster Systems of Elliptical Galaxies

D. Geisler (CTIO), S. Zepf (UC Berkeley), K. Ashman (U. Kansas), W. Harris, D. McLaughlin, J. Secker (McMaster U.)

Integrated photometry on the Washington system has been obtained for the globular cluster systems of two elliptical galaxies: NGC 3311 and NGC 3923. The derived color and magnitude information, combined with image classification, allows us to select cluster candidates with $> 90\%$ confidence. Metal abundances are derived from the very metallicity sensitive $(C-T_1)$ color index for 103 globular cluster candidates in NGC 3311 and 143 candidates in NGC 3923. Analysis of the metallicity distributions indicates the likely presence of two or more peaks. The median metallicity of these two cluster systems is surprisingly high: $-0.56$ for NGC 3923 and $-0.31$ for NGC 3311, making them the most metal-rich cluster systems known. The respective metallicities are significantly higher than predicted by previous relations believed to hold between the metallicity of a cluster system and the luminosity of the parent galaxy. We also detect significant color gradients with galactocentric distance. These results are compared to those for other cluster systems and their significance for theories of galaxy and cluster formation are discussed.

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