Donald Drew Egbert

Venturi, Robert

doi:10.1515/9781400864393.82

Cited by 6 publications

(5 citation statements)

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“…However, the spectral properties of RHs are hard to constrain, because of the observational difficulties in obtaining reliable measurements of RH flux densities spanning a large frequency range. During the last decade it has been found that the observed spectral index, α, of RHs spans a broad range of values: α ∼ 1 − 2, with F (ν) ∝ ν −α (Feretti et al 2012;Venturi, 2011;Venturi et al 2013). This implies that the synchrotron spectrum of RHs is not a universal power law and puts constraints on the mechanisms responsible for the origin of RHs.…”

Section: Resultsmentioning

confidence: 99%

Radio halos in a mass-selected sample of 75 galaxy clusters

Cuciti

Cassano

Brunetti

et al. 2021

A&A

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Context. Radio halos are synchrotron diffuse sources at the centre of a fraction of galaxy clusters. The study of large samples of clusters with adequate radio and X-ray data is necessary to investigate the origin of radio halos and their connection with the cluster dynamics and formation history. Aims. The aim of this paper is to compile a well-selected sample of galaxy clusters with deep radio observations to perform an unbiased statistical study of the properties of radio halos. Methods. We selected 75 clusters with M ≥ 6 × 1014 M⊙ at z = 0.08 − 0.33 from the Planck Sunyaev-Zel’dovich catalogue. Clusters without suitable radio data were observed with the Giant Metrewave Radio Telescope and/or the Jansky Very Large Array to complete the information about the possible presence of diffuse emission. We used archival Chandra X-ray data to derive information on the clusters’ dynamical states. Results. This observational campaign led to the detection of several cluster-scale diffuse radio sources and candidates that deserve future follow-up observations. Here we summarise their properties and add information resulting from our new observations. For the clusters where we did not detect any hint of diffuse emission, we derived new upper limits to their diffuse flux. Conclusions. We have built the largest mass-selected (> 80% complete in mass) sample of galaxy clusters with deep radio observations available to date. The statistical analysis of the sample, which includes the connection between radio halos and cluster mergers, the radio power – mass correlation, and the occurrence of radio halos as a function of the cluster mass, will be presented in Paper II.

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Section: Resultsmentioning

confidence: 99%

Radio halos in a mass-selected sample of 75 galaxy clusters

Cuciti

Cassano

Brunetti

et al. 2021

A&A

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“…In recent years thanks to the improvement in low frequency radio observations, a large attention has been devoted to the search for and discussion of ultra-steep spectrum radio halos (see e.g. [263]).…”

Section: Ultra-steep Spectrum Halosmentioning

confidence: 99%

Clusters of galaxies: observational properties of the diffuse radio emission

Feretti

Giovannini

Govoni

et al. 2012

Astron Astrophys Rev

679

908

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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.

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“…CR electrons are very well traced in the ICM through their radio emission which appears in the form of diffuse (Mpc scale) synchrotron giant radio halos from the cluster X-ray emitting regions, and relics, typically in the clusters' peripheral regions (see Ferrari et al 2008, Venturi 2011, for recent reviews on observations). Giant radio halos are the most spectacular and best studied non-thermal large scale phenomena in the universe.…”

Section: Introductionmentioning

confidence: 99%

Probing the origin of giant radio haloes through radio and γ-ray data: the case of the Coma cluster

Brunetti

Blasi

Reimer

et al. 2012

Monthly Notices of the Royal Astronomical Society

138

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We combine for the first time all available information about the spectral shape and morphology of the radio halo of the Coma cluster with the recent γ -ray upper limits obtained by the Fermi-Large Area Telescope (LAT) and with the magnetic field strength derived from Faraday rotation measures. We explore the possibility that the radio emission is due to synchrotron emission of secondary electrons. First, we investigate the case of pure secondary models that are merely based on the mechanism of continuous injection of secondary electrons via proton-proton collisions in the intracluster medium. We use the observed spatial distribution of the halo's radio brightness to constrain the amount of cosmic ray protons and their spatial distribution in the cluster that are required by the model. Under the canonical assumption that the spectrum of cosmic rays is a power law in momentum and that the spectrum of secondaries is stationary, we find that the combination of the steep spectrum of cosmic ray protons necessary to explain the spectrum of the halo and the very broad spatial distribution (and large energy density) of cosmic rays result in a γ -ray emission in excess of present limits, unless the cluster magnetic field is relatively large. However, this large magnetic field required to not violate present γ -ray limits appears inconsistent with that derived from recent Faraday rotation measures. Secondly, we investigate more complex models in which the cosmic rays confined diffusively in the Coma cluster and their secondary electrons are all reaccelerated by magnetohydrodynamics turbulence. We show that under these conditions it is possible to explain the radio spectrum and morphology of the radio halo and to predict γ -ray fluxes in agreement with the Fermi-LAT upper limits without tension with present constraints on the cluster magnetic field. Reacceleration of secondary particles also requires a very broad cosmic ray spatial profile, much flatter than that of the intracluster medium, at least provided that both the turbulent and magnetic field energy densities scale with that of the intracluster medium. However, this requirement can be easily alleviated if we assume that a small amount of (additional) seed primary electrons is reaccelerated in the cluster's external regions, or if we adopt flatter scalings of the turbulent and magnetic field energy densities with distance from the cluster centre.

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Donald Drew Egbert

Cited by 6 publications

References 0 publications

Radio halos in a mass-selected sample of 75 galaxy clusters

Radio halos in a mass-selected sample of 75 galaxy clusters

Clusters of galaxies: observational properties of the diffuse radio emission

Probing the origin of giant radio haloes through radio and γ-ray data: the case of the Coma cluster

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