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Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. Some of the basic physical properties of mergers will be discussed, with an emphasis on simple analytic arguments rather than numerical simulations. Semi-analytic estimates of merger rates are reviewed, and a simple...
An increasing amount of data has revealed that many clusters are very complex systems. Optical analyses show that several clusters contain subsystems of galaxies, suggesting that they are still in the phase of dynamical relaxation. Indeed, there is a growing evidence that these subsystems arise as the consequence of group/cluster mergers. We here review the state of art of optical search and characterization...
X-ray observations have played a key role in the study of substructure and merging in galaxy clusters. I review the evidence for cluster substructure and mergers obtained from X-ray observations with satellites that operated before Chandra and XMM. Different techniques to study cluster mergers via X-ray imaging and spectral data are discussed with an emphasis on the quantitative analysis of cluster...
Chandra’s high angular resolution has provided a surprising new view of clusters of galaxies. First, we discuss the newly discovered “cold fronts”, sharp, edge-like surface brightness structures in clusters. These sharp features, previously suggested to be shock fronts, probably arise from cluster mergers. We review Chandra observations of merging clusters with radio halos that provide new insights...
In this chapter we focus on the discussion of observational data on cluster mergers. The majority of the results shown comes from observations with the ROSAT observatory. Results from ASCA, BeppoSAX and from very recent observations performed with XMM-Newton are also included. We discuss the signature and diagnostics of the merger process in galaxy clusters. We show some observable effects caused...
In this paper we review the properties of radio galaxies in connection to the effect of the dynamic gaseous environment inside clusters in which they are embedded. The external gas can interact with a radio source in different ways: modifying its morphology via ram-pressure, confining the radio lobes, possibly feeding the active nucleus, enhancing star formation, exerting stripping effects on the...
The historical course in the search of extended halo and relic sources in clusters of galaxies is summarized, and it is shown that only in recent years has a significant improvement in the knowledge of the properties of these sources been reached. The study of diffuse sources is very important in understanding the role of large scale magnetic fields and relativistic particles in the intracluster medium...
Simulations of clusters of galaxies reveal how clusters form and evolve. Models of cluster mergers show many characteristics of these very energetic events: shock structure and strength, temperature variations and gas distribution. Also detailed observational signatures of the dynamical state can be derived from the models. The simulations show that mergers have effects on the magnetic field, on the...
The character of the galaxy cluster population holds clues to the identity of the particular world model that best describes our universe. Although clusters are complex in their fine detail, their dark matter and intracluster medium (ICM) content appear to be well described by relatively simple processes driven by gravitationally induced mergers. After reviewing theoretical frameworks of spherical...
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