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Session 52 - Clusters & Cosmology.
Oral session, Thursday, June 12
North Main Hall C/D,
I discuss the results of a study of the globular cluster systems of 23 bright central galaxies in 19 Abell clusters, concentrating on the newly discovered correlations of the globular cluster specific frequencies S_N in these galaxies with other galaxy and cluster properties. The Abell clusters in this sample range in redshift from 5000 to 10,000 km/s, and were selected from the Lauer amp; Postman (1994) survey of brightest cluster galaxies. The analysis procedure is partly based on the surface brightness fluctuations method. For these galaxies, S_N correlates well with measures of the cluster density, such as velocity dispersion of the cluster galaxies, cluster X-ray temperature and luminosity, and the local density of bright galaxies. S_N correlates less strongly with galaxy profile, and only marginally with galaxy luminosity. Within a cluster, S_N is larger for the more centrally dominant galaxies, judged by position relative to the cluster X-ray center. The scaling of S_N with cluster density suggests that globular clusters formed early and in proportion to the available mass, while the central galaxy luminosity ``saturated'' at a maximum threshold, resulting in higher S_N for central galaxies in denser clusters and the observed insensitivity of galaxy luminosity to cluster richness. The analysis makes the usual assumption that the globular cluster luminosity function is universal, and therefore the apparent magnitude of the turnover is predictable. The implications of this study for the universality assumption will be briefly discussed.
Program listing for Thursday