Globular Clusters in 19 Northern Abell Clusters

Abstract

We study the globular cluster (GC) populations of 21 giant elliptical galaxies in 19 Abell clusters. This method, applied here primarily in the R band, is based on the surface brightness fluctuations technique of extragalactic distance measurement. The sample galaxies range in redshift from 5000 to 10,000 \kms, and were selected primarily from the Lauer & Postman (1994) survey of brightest cluster galaxies (BCGs). We find a tight correlation between the GC specific frequency S_N of the central bright galaxy in the cluster and the cluster velocity dispersion. S_N also correlates well with the cluster X-ray temperature and with the number of bright neighboring galaxies, less well with the galaxy profile, and only marginally with galaxy luminosity and overall cluster richness. It does not correlate with cluster morphology class. Thus, unlike galaxy luminosity, S_N is determined by the cluster mass, or density. To account for this situation, we propose that the GCs formed early and in proportion to the available mass, while the luminosity growth of the galaxy was later halted, yielding the observed correlations of S_N with density. We introduce a quantity called $η_{GC}$, the number of GCs per unit local cluster mass. For a simple cluster mass model, $η_{GC}$ is found to be constant, indicating a uniform GC production rate per unit available mass. A measurement of the Gaussian width $σ$ of the GC luminosity function (GCLF) is one of the byproducts of our analysis. In the cosmic microwave background frame, the mean width for this sample is $< σ> = 1.43$ mag, virtually identical to the HST value for M87, the galaxy used to calibrate the mean of the GCLF in this analysis.