The Fraction of Cool-core Clusters in X-Ray versus SZ Samples Using Chandra Observations

作者：Andrade Santos Felipe^*; Jones Christine; Forman William R; Lovisari Lorenzo; Vikhlinin Alexey; van Weeren Reinout J; Murray Stephen S; Arnaud Monique; Pratt Gabriel W; Democles Jessica; Kraft Ralph; Mazzotta Pasquale; Boehringer Hans; Chon Gayoung; Giacintucci Simona; Clarke Tracy E; Borgani Stefano; David Larry; Douspis Marian; Pointecouteau Etienne; Dahle Hakon; Brown Shea; Aghanim Nabila; Rasia Elena

来源：Astrophysical Journal, 2017, 843(1): 76.

DOI：10.3847/1538-4357/aa7461

• galaxies: clusters: general
• large-structure of universe

We derive and compare the fractions of cool-core clusters in the Planck Early Sunyaev-Zel'dovich sample of 164 clusters with z <= 0.35 and in a flux-limited X-ray sample of 100 clusters with z <= 0.30, using Chandra observations. We use four metrics to identify cool-core clusters: (1) the concentration parameter, which is the ratio of the integrated emissivity profile within 0.15 r(500) to that within r(500); (2) the ratio of the integrated emissivity profile within 40 kpc to that within 400 kpc; (3) the cuspiness of the gas density profile, which is the negative of the logarithmic derivative of the gas density with respect to the radius, measured at 0.04 r(500); and (4) the central gas density, measured at 0.01 r(500). We find that the sample of X-ray-selected clusters, as characterized by each of these metrics, contains a significantly larger fraction of cool-core clusters compared to the sample of SZ-selected clusters (44% +/- 7% versus 28% +/- 4% using the concentration parameter in the 0.15-1.0 r(500) range, 61% +/- 8% versus 36% +/- 5% using the concentration parameter in the 40-400 kpc range, 64% +/- 8% versus 38% +/- 5% using the cuspiness, and 53% +/- 7% versus 39 +/- 5% using the central gas density). Qualitatively, cool-core clusters are more X-ray luminous at fixed mass. Hence, our X-ray, flux-limited sample, compared to the approximately mass-limited SZ sample, is overrepresented with cool-core clusters. We describe a simple quantitative model that uses the excess luminosity of cool-core clusters compared to non-cool-core clusters at fixed mass to successfully predict the observed fraction of cool-core clusters in X-ray-selected samples.

• 出版日期2017-7-1
• 单位中国地震局