Temperature and entropy profiles of nearby cooling flow clusters observed with XMM-Newton

Abstract

Abstract. We investigate temperature and entropy profiles of 13 nearby cooling flow clusters observed with the EPIC cameras of XMM-Newton. When normalized and scaled by the virial radius the temperature profiles turn out to be remarkably similar. At large radii the temperature profiles show a clear decline starting from a break radius at ∼0.1 r vir . The temperature decreases by ∼30% between 0.1 r vir and 0.5 r vir . As expected for systems where non-gravitational processes are of great importance, the scale length characterizing the central temperature drop is not found to be proportional to the virial radius of the system. The entropy of the plasma increases monotonically moving outwards almost proportional to the radius and the central entropy level is tightly correlated with the core radius of the X-ray emission. The dispersion in the entropy profiles is smaller if the empirical relation S ∝ T 0.65 is used instead of the standard self-similar relation S ∝ T and, as expected for cooling flow clusters, no entropy cores are observed.

Thermodynamical Properties of the ICM from Hydrodynamical Simulations

“…Indications from ASCA data showed that entropy profiles of poor clusters and groups have an amplitude which is higher than that expected for rich clusters from the above scaling argument. This result has been subsequently confirmed by the XMM-Newton data analysed by Pratt and Arnaud (2005) and by Piffaretti et al (2005). Quite remarkably, a relatively higher entropy for groups is found not only in the central regions, where it can arise as a consequence of the heating/cooling processes, but extends to all radii sampled by X-ray observations, out to 0.5r 500 .…”

“…The much improved sensitivity of the Chandra satellite provides now a more detailed picture of the central temperature profiles (e.g., Baldi et al 2007). At the same time, a number of analyses of XMM-Newton observations now consistently show the presence of a negative gradient at radii 0.1r 200 (e.g., Piffaretti et al 2005;Pratt et al 2007, and references therein). Relaxed clusters are generally shown to have a smoothly declining profile toward the centre, reaching values which are about half of the overall virial cluster temperature in the innermost sampled regions, with non-relaxed clusters having, instead, a larger variety of temperature profiles.…”

“…The steeper slope of the L X -T relation (Markevitch 1998;Arnaud and Evrard 1999;Osmond and Ponman 2004), L X ∝ T α with α 3 for clusters and possibly larger for groups, the excess entropy in poor clusters and groups Pratt and Arnaud 2005;Piffaretti et al 2005) and the decreasing trend of the gas mass fraction in poorer systems (Lin et al 2003; all point toward the presence of some mechanism which significantly affects the ICM thermodynamics.…”

“…The crosses with error bars are observational data on the entropy measured at one-tenth of the virial radius for clusters and groups by Ponman et al (1999). Right panel: a comparison between observations (error bars with crosses; Ponman et al (1999) and simulations, including radiative cooling and star formation (numbers), for the entropy in the central regions of galaxy groups and clusters. The solid line shows the prediction of the self-similar model (from Davé et al 2002) Although it may look like a paradox, radiative cooling has been also suggested as a possible alternative to non-gravitational heating to increase the entropy level of the ICM and suppressing the gas content in poor systems.…”

“…2 Left panel: the relation between entropy and temperature for gas having a fixed value of the cooling time (from Voit and Bryan 2001). The crosses with error bars are observational data on the entropy measured at one-tenth of the virial radius for clusters and groups by Ponman et al (1999). Right panel: a comparison between observations (error bars with crosses; Ponman et al (1999) and simulations, including radiative cooling and star formation (numbers), for the entropy in the central regions of galaxy groups and clusters.…”