GLOBULAR-CLUSTER SYSTEM IN 3 CD GALAXIES WITHIN RICH ABELL CLUSTERS

We present new CCD photometry from the CFH telescope for three cD galaxies that are the centrally dominant objects in the rich Abell clusters A2052, A2107, and A2666. Photometry to I(lim) = 25.0 reveals the existence of globular cluster populations around all three of these: the first two appear to have M87-like high specific frequencies around S(N) congruent-to 16, but the third has a normal or subnormal value S(N) congruent-to 3. With these new data, globular cluster systems have now been searched for in a total of 12 centrally dominant cD galaxies in a wide range of galaxy clusters. We find that neither S(N) nor the cluster population are correlated with any known property of the hot intracluster gas that usually surrounds such galaxies (cooling flow rate, gas temperature, total X-ray luminosity, etc.). From this, we conclude that cooling flows at the present epoch (i.e., in the last few Gyr) have little or nothing to do with globular cluster formation. The recently formed globular clusters in the central regions of such galaxies as NGC 1275 seem, instead, to be the result of occasional starburst phenomena. The vastly larger old-cluster populations filling the outer halos of many cD galaxies must be the result of an intensive phase of cluster formation during the very early protogalactic epoch.