Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-06-20
Astronomy and Astrophysics
Astrophysics
MNRAS in press - Minor revision to match the accepted version
Scientific paper
10.1111/j.1365-2966.2007.12158.x
[Abridged] The entropy distribution of the intracluster gas reflects both accretion history of the gas and processes of feedback which provide a further non-gravitational energy besides the potential one. In this work, we study the profiles and the scaling properties of the gas entropy in 24 hot (kT_{gas} > 6 keV) galaxy clusters observed with Chandra in the redshift range 0.14-0.82 and showing different states of relaxation. We recover the gas density, temperature and entropy profiles in a non-parametric way. Adding the hydrostatic equilibrium hypothesis, radial profiles are also obtained from the deprojection of the surface brightness, allowing to verify whether the hydrostatic equilibrium is a tenable hypothesis by comparison with the spectral measurements. We confirm that this is the case on scales larger than 100 kpc and discuss the deviations observed in few non-cooling core clusters in the inner regions. We show that the entropy profiles are remarkably similar outside the core and can be described by simple power-laws with slope of 1.0-1.2. We measure an entropy level at 0.1 R_{200} of 100-500 keV cm^2 and a central plateau which spans a wide range of value (~ a few-200 keV cm^2) depending on the state of relaxation of the source. To characterize the energetic of the central regions, we compare the radial behaviour of the temperature of the gas with the temperature of the dark matter T_{DM} by estimating the excess of energy Delta E = 3/2 k(T_{gas}- T_{DM}). We point out that Delta E ranges from ~ 0 in typical cooling-core clusters to few keV within 100 kpc in non-cooling core systems. We also measure a significant correlation between the total iron mass and the entropy outside the cooling region,whereas in the inner regions they anti-correlate strongly.
Ettori Stefano
Morandi Andrea
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