Clusters of galaxies: observational properties of the diffuse radio emission

By L. Feretti, G. Giovannini, F. Govoni, M. Murgia. The Astronomy and Astrophysics Review, 2012

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/21e62a99239fed4ee294592e397f7a674f2f8506

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Citations in the corpus

• The case for electron re-acceleration at galaxy cluster shocks (2017, methodology): “We fitted the surface brightness profile in an elliptical sector that crosses the radio relic (see the Supplementary Information), using the model given in equation (1).”
• Diffuse Radio Emission from Galaxy Clusters (2019, background): “Similar to radio halos, a correlation is found between cluster X-ray luminosity and radio power of cluster radio shocks (Feretti et al. 2012).”
• The LOFAR Two-metre Sky Survey. I. Survey description and preliminary data release (2016, background): “In approximately 100 galaxy clusters diffuse steep spectrum synchrotron emission that is associated with the intra-cluster medium (ICM) has been observed (see Ferrari et al. 2008, Brüggen et al. 2012, Feretti et al. 2012 and Brunetti & Jones 2014 for recent reviews).”
• Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, background): “Also the magnetic fields in clusters are of the order of µGauss (Clarke et al 2001; Bonafede et al 2010; Feretti et al 2012).”
• The GMRT 150 MHz all-sky radio survey - First alternative data release TGSS ADR1 (2016, background): “Propagation phenomena in the magneto-ionized medium of our galaxy are stronger (Stovall et al. 2015), galaxy clusters show extended relics and halos (Feretti et al. 2012), and both AGN and radio Article published by EDP Sciences A78, page 1 of 28 galaxies show evidence of earlier phases of activity…”
• SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS (2013, background): “In fact, elongated relics show a mean radio spectral index of 〈αν〉 = 1.3 (Feretti et al. 2012), which translates to a cooling-corrected spectral index of CR electrons of α = 2αν = 2.6 (which is a lower limit since the uncorrected injection index could be as high as α = 2αν + 1 = 3.6).”
• Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, unknown): “Large-scale magnetic fields are also probed in galaxy clusters, both through the measurement of the Faraday rotation effect on the light of background galaxies and through radio emission from the halos and relics of the clusters (Govoni & Feretti 2004; Ferrari et al. 2008; Feretti et al. 2012).”
• Radio galaxies and feedback from AGN jets (2020, background): “For a detailed review of these diffuse cluster radio sources, see Feretti et al. (2012). Particle acceleration models for diffuse radio sources in clusters suggest that a seed population of relativistic particles is required to produce the observed ex-”
• The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science Case and Survey Design (2019, background): “For example, extended FRI sources for “radio mode” feedback in groups and clusters (e.g., Feretti et al. 2012; Clarke et al. 2014; Russell et al. 2017) (visible out to z ≈ 0.5), and powerful, compact sources for “quasar mode” feedback and interactions between jets and ionized gas in compact radio…”