Evolution of Cluster X-Ray Luminosities and Radii: Results from the 160 Square Degree ROSAT Survey

We searched for cluster X-ray luminosity and radius evolution using our sample of 203 galaxy clusters detected in the 160 deg² survey with the ROSAT PSPC (Vikhlinin et al.). With such a large area survey, it is possible, for the first time with ROSAT, to test the evolution of luminous clusters, L_X > 3 × 10⁴⁴ ergs s⁻¹ in the 0.5-2 keV band. We detect a factor of 3-4 deficit of such luminous clusters at z > 0.3 compared with the present. The evolution is much weaker or absent at modestly lower luminosities, (1-3) × 10⁴⁴ ergs s⁻¹. At still lower luminosities, we find no evolution from the analysis of the log N-log S relation. The results in the two upper L_X bins are in agreement with the Einstein Extended Medium-Sensitivity Survey evolution result (Gioia et al.; Henry et al.), which was obtained using a completely independent cluster sample. The low-L_X results are in agreement with other ROSAT surveys (e.g., Rosati et al.; Jones et al.). We also compare the distribution of core radii of nearby and distant (z > 0.4) luminous (with equivalent temperatures of 4-7 keV) clusters and detect no evolution. The ratio of average core radius for z ~0.5 and z < 0.1 clusters is 0.9 ± 0.1, and the core radius distributions are remarkably similar. A decrease of cluster sizes incompatible with our data is predicted by self-similar evolution models for a high-Ω universe.