A statistically selected Chandra sample of 20 galaxy clusters -: I.: Temperature and cooling time profiles

We present an analysis of 20 galaxy clusters observed with the Chandra X-ray satellite, focusing on the temperature structure of the intracluster medium and the cooling time of the gas. Our sample is drawn from a flux-limited catalogue but excludes the Fornax, Coma and Centaurus clusters, owing to their large angular size compared to the Chandra field of view. We describe a quantitative measure of the impact of central cooling, and find that the sample comprises nine clusters possessing cool cores (CCs) and 11 without. The properties of these two types differ markedly, but there is a high degree of uniformity amongst the CC clusters, which obey a nearly universal radial scaling in temperature of the form T alpha r(similar to 0.4), within the core. This uniformity persists in the gas cooling time, which varies more strongly with radius in CC clusters (t(cool) alpha r(similar to 1.3)), reaching t(cool) < 1 Gyr in all cases, although surprisingly low central cooling times (< 5 Gyr) are found in many of the non-CC systems. The scatter between the cooling time profiles of all the clusters is found to be remarkably small, implying a universal form for the cooling time of gas at a given physical radius in virialized systems, in agreement with recent previous work. Our results favour cluster merging as the primary factor in preventing the formation of CCs.