Astronomy & Astrophysics

A&A 446, 429-438 (2006)
DOI: 10.1051/0004-6361:20054025

Structure and scaling of the entropy in nearby galaxy clusters

G. W. Pratt¹, M. Arnaud² and E. Pointecouteau^{2, 3}

¹ MPE Garching, Giessenbachstraße, 85748 Garching, Germany
e-mail: gwp@mpe.mpg.de
² CEA/Saclay, Service d'Astrophysique, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
³ Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK

(Received 10 August 2005 / Accepted 22 September 2005)

Abstract
Using XMM-Newton observations, we investigate the scaling and structural properties of the ICM entropy in a sample of 10 nearby (z < 0.2) morphologically relaxed galaxy clusters in the temperature range 2-9 keV. We derive the local entropy-temperature (S-T) relation at R = 0.1, 0.2, 0.3 and 0.5R₂₀₀. The logarithmic slope of the relation is the same within the $1\sigma$ error at all scaled radii. However, the intrinsic dispersion about the best fitting relation is significantly higher at 0.1R₂₀₀. The slope is $0.64\pm0.11$ at $0.3\,R_$ , in excellent agreement with previous work. We also investigate the entropy-mass relation at density contrasts $\delta=5000, 2500$ and 1000. We find a shallower slope than that expected in simple self-similar models, which is in agreement with the observed empirically-determined entropy-temperature and mass-temperature scaling. The dispersion is smaller than for the S-T relation. Once scaled appropriately, the entropy profiles appear similar beyond ~ 0.1R₂₀₀, with an intrinsic dispersion of ~15 per cent and a shape consistent with gravitational heating ( $S(r) \lower 3pt \hbox{$\, \buildrel {\textstyle \propto}\over {\textstyle \sim}\,$ }r^$ ). However, the scatter in scaled entropy profiles increases with smaller scaled radius, to more than 60 per cent at $R \la 0.05 R_$ . Our results are in qualitative agreement with models which boost entropy production at the accretion shock. However, localised entropy modification may be needed to explain the dispersion in the inner regions.

Key words: cosmology: observations -- galaxies: intergalactic medium -- X-rays -- galaxies: clusters

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