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L. Feretti etal. (eds.), Merging Processes in Galaxy Clusters, 229-251. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.

observations" one can for example distinguish which observable feature corresponds to which dynamical state. Moreover, observational methods can be tested with the simulated data. The results can be compared to the input parameters of the calculations and, in an iterative procedure, the methods can be refined. In this way not only can physical processes in clusters and on larger scales be understood, but there is also an opportunity to constrain cosmological models.

Merging of subclusters is a particularly interesting phenomenon to study with simulations. Irregular cluster morphologies in cluster X-ray images as well as indications from optical observations suggest that many clusters are not relaxed. Hence major mergers and the infall of smaller structures are quite common in clusters of galaxies. Such mergers of subclusters are very energetic events, which affect clusters strongly, e.g. shocks emerge. These shocks are important for the conditions in clusters because they are the major heating source for the intra-cluster gas. Moreover particles can be (re-)accelerated in these shock waves. Numerical models are ideal to reveal where shocks emerge, where they move to and how strong they are.

This article is structured as follows. In § 1 the simulation methods are explained briefly. After some general features of the models (§ 2) the effects of mergers are discussed in § 3. § 4 lists additional physical processes: cooling, star formation and magnetic fields. In § 5 the connection between mergers and the metallicity of the intra-cluster gas is reviewed. The mass determination in merging clusters is discussed in § 6. A summary is given in § 7.

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