ON THE DISTRIBUTION OF RADIO-SOURCES IN RICH GALAXY CLUSTERS

The radial surface density distribution of Molonglo radio sources in rich southern Abell clusters reported by Robertson & Roach is shown to follow very precisely over a three dex range the r1/4 law with an effective radius of R(e) = 100 kpc and an effective surface density of 0.333 radio source Mpc-2. There is no need to postulate a two-component distribution. Comparison with the known effective radii of a few rich northern clusters ( almost-equal-to kpc) suggests that the radio source distribution is much more concentrated to the cluster centres than the radio-quiet members. In any case, this is one more example of the validity of an empirical formula applicable to a large class of objects (stars in elliptical galaxies and bulges of spirals, globular clusters in E and S galaxies, galaxies in rich clusters), all resulting presumably from the collapse of a system of collisionless 'particles' (stars, clusters, galaxies).