Simulations of X-ray clusters

Abstract

We present simulations of the formation and evolution of galaxy clusters in\nthe Cold Dark Matter cosmogony. Clusters with a wide range of mass were\nselected from previous N-body models, and were resimulated at higher resolution\nusing a combined N-body/Smooth Particle Hydrodynamics code. The effects of\nradiative cooling on the gas are neglected. While many present-day clusters are\npredicted to be undergoing mergers, the density profiles of those that are\napproximately in equilibrium are all very similar, both for the gas and for the\ndark matter. These profiles show no sign of a uniform density core and steepen\ngradually from the centre outwards. The standard $\\beta$-model is a reasonable\nfit over most of the radius range observable in real clusters. However, the\nvalue obtained for the slope parameter $\\beta_f$ increases with the outermost\nradius of the fit. Temperature profiles of different simulated clusters are\nalso similar. Typically the temperature is almost uniform in the regions which\nemit most of the X-ray flux but drops at larger radii. The gas temperature and\ndark matter velocity dispersion in equilibrium clusters give values of\n$\\beta_T\\equiv \\mu m_p\\sigma_{DM}^2/kT$ which are consistent with unity\nprovided an X-ray emission-weighted temperature is used. Larger values of\n$\\beta_T$ are found in merging objects where there is a transient boost in the\nvelocity dispersion of the system. Thus $\\beta_T >1$ may be an observational\nindicator of merging in real clusters. The similar structure of clusters of\ndiffering mass results in scaling relations between the X-ray and dynamical\nproperties of clusters identified at\n

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Affiliated Institutions

• Institute of Astronomy RU
• Durham University GB

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