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) α , 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 ≈ 30–50 keV cm 2 and population peaks at K 0 ∼ 15 keV cm 2 and K 0 ∼ 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 For completeness, we include previously unpublished optical spectroscopy of Hα and [N ii ] emission lines discussed in Cavagnolo et al.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.