Thermodynamic profiles of galaxy clusters from a joint X-ray/SZ analysis

Abstract

We jointly analyse the Bolocam Sunyaev–Zel’dovich (SZ) effect and Chandra X-ray data for a set of 45 clusters to derive gas density and temperature profiles without using spectroscopic information. The sample spans the mass and redshift range 3×1014 M_☉ ≤ M₅₀₀ ≤ 25 × 1014 M_☉ and 0.15 ≤ z ≤ 0.89. We define cool-core and non-cool core subsamples based on the central X-ray luminosity, and 17 out of 45 clusters are classified as cool core. In general, the profiles derived from our analysis are found to be in good agreement with previous analyses, and profile constraints beyond r₅₀₀ are obtained for 34 out of 45 clusters. In approximately 30 per cent of the cool-core clusters, our analysis shows a central temperature drop with a statistical significance of >3σ; this modest detection fraction is due mainly to a combination of coarse angular resolution and modest signal-to-noise ratio in the SZ data. Most clusters are consistent with an isothermal profile at the largest radii near r₅₀₀, although 10 out of 45 show a significant temperature decrease with increasing radius. The sample mean density profile is in good agreement with previous studies, and shows a minimum intrinsic scatter of approximately 10 per cent near 0.5r₅₀₀. The sample mean temperature profile is consistent with isothermal, and has an intrinsic scatter of approximately 50 per cent  independent of radius. This scatter is significantly higher compared to earlier X-ray-only studies, which find intrinsic scatters near 10 per cent , likely due to a combination of unaccounted-for non-idealities in the SZ noise, projection effects, and sample selection.

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