Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-09-11
Mon.Not.Roy.Astron.Soc. 323 (2001) 930
Astronomy and Astrophysics
Astrophysics
10 pages, 5 figures, submitted to MNRAS. abstract abriged
Scientific paper
10.1046/j.1365-8711.2001.04286.x
The temperature profile (TP) of the intracluster medium (ICM) is of primeval importance for deriving the dynamical parameters of the largest equilibrium systems known in the universe, in particular their total mass profile. Analytical models of the ICM often assume that the ICM is isothermal or parametrize the TP with a polytropic index. This parameter is ajusted to observations, but has in fact poor physical meaning for values other than 1 or 5/3, when considering monoatomic gases. In this article, I present a theoretical model of a relaxed cluster where the TP is instead structured by electronic thermal conduction. Neglecting cooling and heating terms, the stationnary energy conservation equation reduces to a 2nd order differential equation, whose resolution requires two boundary conditions, taken here as the inner radius and the ratio between inner and outer temperature. Once these two constants are chosen, the TP has a fixed analytical expression, which reproduces nicely the observed ``universal'' TP obtained by Markevitch et al. (1998) from ASCA data. Using observed X-ray surface brightnesses for two hot clusters with spatially resolved TP, the local polytropic index and the hot gas fraction profile are predicted and compare very well with ASCA observations (Markevitch et al 1999). Moreover, the total density profile derived from observed X-ray surface brightness, hydrostatic equilibrium and the conduction-driven TP is very well fit by three analytical profiles found to describe the structure of galactic or cluster halos in numerical simulations of collisionless matter (Hernquist, 1991; Navarro et al. 1995, 1997; Burkert 1995). (abriged)
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