Core radii and mass segregation in clusters of galaxies

Abstract

Isothermal models are fitted to recent data on the Coma and CA 0340-538 clusters. Series of models are obtained for various magnitude limits. In both clusters it is found that the derived core radii are significantly dependent on those limits: They increase by about a factor of 2 when the magnitude increases from about M/sub asterisk/ (the magnitude at the ''knee'' of the luminosity function) to 2--4 magnitudes fainter. The influence on the models of the assumed background, cluster centers, halo, and ring size is investigated. The core radii do not seem very dependent on these parameters. These results seem to imply that more mass segregation than is usually recognized is present, at least in some clusters. Additionally, the Coma cluster shows a narrow density peak centered somewhere within 0.1 Mpc of NGC 4874, and about 0.15 Mpc in radius, which is present essentially at all magnitude levels. The central density is about 1.5--2 times the value predicted by the model. This feature may indicate the presence of a dynamically separated subunit.