RADIO OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES AND ITS IMMEDIATE VICINITY .3. STATISTICAL-ANALYSES AND SOURCE COUNTS

A statistical analysis of the properties of radio sources in a 7-degre es x 7-degrees field centred on the Coma cluster of galaxies is presen ted, based on new observations. Unlike optical galaxies, radio sources are not highly concentrated towards the centre of the cluster, but th ere appears to be a small excess of sources at the periphery. Attempts to detect clustering of radio sources using the angular covariance fu nction have produced a null result over all angular scales. The lack o f a strong concentration of radio sources near the cluster centre sugg ests that galaxy number density is not the primary condition which det ermines the likelihood of a galaxy becoming a strong radio emitter. St atistical tests show there is no significant difference between the ga laxy population around radio galaxies and that around non-radio galaxi es in the cluster, suggesting that neither cluster related gravitation al interactions nor interactions with the intra-cluster medium enhance the probability of formation of radio galaxies. In fact, the cluster environment seems to suppress the strong radio galaxy phenomenon. Radi o source counts at 408 MHz, which have a limiting flux density of 80 m Jy, are not significantly different from counts of non-cluster backgro und sources. However, a deep source count at 1380 MHz over the central region of the cluster shows an excess in number of sources when the f lux density limit is 1 mJy, suggesting that the cluster environment ma y induce some radio emission in galaxies, but that this emission is un likely to be strong. The number of radio sources in the central region of the cluster which might in the future be optically identified is 1 5 +/- 5. Sources seen near the cluster centre show a marginally signif icant tendency to have steeper spectral indices than those at greater distance. Sources showing extended structure and downward curvature in their high-frequency spectra are found exclusively in the inner regio n of the cluster. These are considered to be sources confined by the i ntra-cluster medium in which spectral steepening at high frequencies i s due to depletion of high-energy electrons.