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Investigating similarity-breaking in galaxy clusters with XMM-Newton and Chandra


If galaxy clusters, containing 80% dark matter, formed hierarchically under the influence of gravity alone, we would expect their intrinsic properties to follow self-similar scaling derived, assuming hydrostatic equilibrium, from basic viral relations. Such similarity applies equally to the hot X-ray emitting intra-cluster medium and thedark matter components. For instance, the total mass would be proportional to the X-ray temperature (M µ T³/²) and the X-ray luminosity would be proportional to the square of the X-ray temperature (Lx µ T²). While observations of the ICM have shown that there is an obvious similarity in the form of the gas temperature and density profiles, the scaling relations break down in the low mass limit. That real clusters do not follow the expected scaling laws points to the influence of non-gravitational processes during their formation. That the similarity breaking occurs in the low mass limit implies that here, the non-gravitational processes affect the properties of the ICM in direct competition with gravity. I propose to use high-quality XMM-Newton and Chancre data to attack the question of why galaxy clusters donor follow the expected scaling relations. Radial temperature, density, chemical abundance, mass and entropy profiles will be obtained for a large sample of clusters across a wide mass/temperature range. Such a sample will allow a global and integrated approach to testing the current theories of non-gravitational input presumed responsible for modifying the observed scaling properties. In particular, I will be able to test whether the dark matter component is collision or non-collision, and investigate he non-gravitational energy input through examination of the entropy and chemical abundance profiles. The project will make extensive use of the European Space Agency's XMM-Newton satellite, and will entail collaboration with a number of other European institutes.

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