Clusters of galaxies: observational properties of the diffuse radio emission
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.
- Clusters of galaxies: observational properties of the diffuse radio emission
- Open Access
- Available under Open Access This content is freely available online to anyone, anywhere at any time.
The Astronomy and Astrophysics Review
- Online Date
- May 2012
- Print ISSN
- Online ISSN
- Additional Links
- Galaxy groups, clusters, and superclusters
- Large scale structure of the Universe
- Galaxy clusters
- Radio sources
- Intracluster matter
- Cooling flows
- Large-scale magnetic fields
- Author Affiliations
- 1. INAF Istituto di Radioastronomia, via Gobetti 101, 40129, Bologna, Italy
- 2. Dipartimento di Astronomia, via Ranzani 1, 40127, Bologna, Italy
- 3. INAF Osservatorio Astronomico di Cagliari, Strada 54, Loc. Poggio dei Pini, 09012, Capoterra (Ca), Italy