On the different radio source populations in the Butcher-Oemler clusters Abell 2125 and 2645

The Abell clusters 2125 and 2645 have different radio source populations, d espite being very similar in richness (Abell class 4) and redshift (similar to 0.25). The number density of radio sources in Abell 2125 is almost an o rder of magnitude more than that in Abell 2645, based on observations to th e same optical and radio luminosities of the two clusters. About 30% of the radio sources in Abell 2125 shows signs of star formation, with the larges t concentration of them in the southwest clump 2 Mpc from the cluster cente r. There is a bimodal distribution of Abell 2125 members in radio luminosit y, with the majority below a spectral luminosity at 20 cm of 10(23) W HZ(-1 ) This entire low-luminosity class of galaxies is absent in Abell 2645. Bas ed on earlier observations, the blue galaxy fractions in Abell 2125 and Abe ll 2645 are known to be 0.19 and 0.03, respectively. Most of the blue galax ies responsible for the Butcher-Oemler effect in Abell 2125 were not detect ed in radio to a 20 cm luminosity limit of 1.4 x 10(22) W HZ-l. The current supernova rate in these blue galaxies is unlikely to be more than a few ti mes the current Galactic supernova rate. The different dynamical states of the two clusters might be responsible for the differences in the radio sour ce populations observed in these two clusters, as well as the Butcher-Oemle r effect.