Abstract
Clusters of galaxies, as the largest virialized systems in the Universe, are ideal laboratories to study the formation and evolution of cosmic structures. The luminous matter of clusters consists of galaxies and of an embedding intracluster medium (ICM), which has been heated to temperatures of tens of millions degrees, and thus is detected through its thermal emission in the soft X-ray regime. Most of the detailed knowledge of galaxy clusters has been obtained in recent years from the study of ICM through X-ray Astronomy. At the same time, radio observations have proved that the ICM is mixed with non-thermal components, i.e. highly relativistic particles and large-scale magnetic fields, detected through their synchrotron emission. The knowledge of the properties of these non-thermal ICM components has increased significantly, owing to sensitive radio images and to the development of theoretical models. Diffuse synchrotron radio emission in the central and peripheral cluster regions has been found in many clusters. Moreover large-scale magnetic fields appear to be present in all galaxy clusters, as derived from Rotation Measure (RM) studies. Non-thermal components are linked to the cluster X-ray properties, and to the cluster evolutionary stage, and are crucial for a comprehensive physical description of the intracluster medium. They play an important role in the cluster formation and evolution. We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos. We discuss their classification and properties. We report published results up to date and obtain and discuss statistical properties. We present the properties of large-scale magnetic fields in clusters and in even larger structures: filaments connecting galaxy clusters. We summarize the current models of the origin of these cluster components, and outline the improvements that are expected in this area from future developments thanks to the new generation of radio telescopes.
Highlights
Clusters of galaxies are the largest gravitationally bound systems in the Universe, with typical masses of about 1015 Msun, and volumes of about 100 Mpc3
We review here the observational properties of diffuse non-thermal sources detected in galaxy clusters: halos, relics and mini-halos
The aim of this review is to present the observational results obtained in recent years in the radio domain related to the diffuse radio sources, in order to give an overview of the state of the art of the current knowledge of non-thermal cluster components
Summary
Clusters of galaxies are the largest gravitationally bound systems in the Universe, with typical masses of about 1015 Msun, and volumes of about 100 Mpc. Non-thermal components are important for a comprehensive physical description of the intracluster medium in galaxy clusters, and play a major role in the evolution of large-scale structures in the Universe They can have dynamic and thermodynamic effects: magnetic fields affect the heat conduction in the ICM and the gas dynamics, relativistic particles are sources of additional pressure and undergo acceleration processes that can modify the details of the ICM heating process. The aim of this review is to present the observational results obtained in recent years in the radio domain related to the diffuse radio sources, in order to give an overview of the state of the art of the current knowledge of non-thermal cluster components. Values taken from the literature have been scaled to this cosmology
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