INTRACLUSTER MEDIUM ENTROPY PROFILES FOR A CHANDRA ARCHIVAL SAMPLE OF GALAXY CLUSTERS

We present radial entropy profiles of the intracluster medium (ICM) for a collection of 239 clusters taken from the Chandra X-ray Observatory's Data Archive. Entropy is of great interest because it controls ICM global properties and records the thermal history of a cluster. Entropy is therefore a useful quantity for studying the effects of feedback on the cluster environment and investigating any breakdown of cluster self-similarity. We find that most ICM entropy profiles are well fitted by a model which is a power law at large radii and approaches a constant value at small radii: K(r) = K-0 + K-100(r/100 kpc)(alpha), where K-0 quantifies the typical excess of core entropy above the best-fitting power law found at larger radii. We also show that the K-0 distributions of both the full archival sample and the primary Highest X-Ray Flux Galaxy Cluster Sample of Reiprich (2001) are bimodal with a distinct gap between K-0 approximate to 30-50 keV cm(2) and population peaks at K-0 similar to 15 keV cm(2) and K-0 similar to 150 keV cm(2). The effects of point-spread function smearing and angular resolution on best-fit K-0 values are investigated using mock Chandra observations and degraded entropy profiles, respectively. We find that neither of these effects is sufficient to explain the entropy-profile flattening we measure at small radii. The influence of profile curvature and number of radial bins on best-fit K-0 is also considered, and we find no indication that K-0 is significantly impacted by either. For completeness, we include previously unpublished optical spectroscopy of H alpha and [N II] emission lines discussed in Cavagnolo et al. (2008a). All data and results associated with this work are publicly available via the project Web site.