The halo and magnetic field of the Coma cluster of galaxies

Kim, K.T.; Kronberg, P. P.; Dewdney, P. E.; Landecker, T. L.

doi:10.1086/168737

Cited by 255 publications

(258 citation statements)

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“…Equipartition or minimum total (relativistic particles plus fields) energy arguments imply a population of relativistic electrons with Lorentz factor γ ∼ 10 4 and magnetic field strength of B ∼ µG, in rough agreement with the Faraday rotation measurements (e.g. Kim et al 1990). Rephaeli (1979) and Schlickeiser et al (1987) also pointed out that the electrons responsible for the radio emission, should also produce a spectrum of hard X-ray (HXR) photons (similar to that observed in the radio band), via inverse Compton (IC) scattering of the Cosmic Microwave Background (CMB) photons.…”

Section: Introductionsupporting

confidence: 78%

“…We assume some proportional relation (e.g. equipartition) between the energies of the magnetic field and non-thermal electrons Allen & Fabian (1998), except 1ES 0657 − 55.8 data from Liang et al (2000) b Data for Coma from Kim et al (1990); A 2256, A 2163, A 1914 and A 2744 from Giovannini et al (1999); 1ES 0657 − 55.8 from Liang et al (2000); A 2219 from Bacchi et al (2003). c Approximate largest angular extent.…”

Section: Hard X-ray and Radio Emissionmentioning

confidence: 99%

“…However, the relatively high observed HXR fluxes require a large number of relativistic electrons, and consequently a relatively low magnetic field for a given observed radio flux. For Coma, this requires the (volume averaged) magnetic field to beB ∼ 0.1 − 0.3 µG, while equipartition givesB ∼ 0.4 µG and Faraday rotation measurements give the (average line-of-sight) field ofB ∼ 3 µG (Giovannini et al 1993;Kim et al 1990;Clarke et al 2001;Clarke 2003). In general the Faraday rotation measurements of most clusters give B > 1 µG; see e.g.…”

Section: Introductionmentioning

confidence: 99%

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Nonthermal Radiation Mechanisms

2008

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In this paper we review the possible radiation mechanisms for the observed non-thermal emission in clusters of galaxies, with a primary focus on the radio and hard X-ray emission. We show that the difficulty with the non-thermal, non-relativisitic Bremsstrahlung model for the hard X-ray emission, first pointed out by Petrosian (2001) using a cold target approximation, is somewhat alleviated when one treats the problem more exactly by including the fact that the background plasma particle energies are on average a factor of 10 below the energy of the non-thermal particles. This increases the lifetime of the non-thermal particles, and as a result decreases the extreme energy requirement, but at most by a factor of three. We then review the synchrotron and so-called inverse Compton emission by relativistic electrons, which when compared with observations can constrain the value of the magnetic field and energy of relativistic electrons. This model requires a low value of the magnetic field which is far from the equipartition value. We briefly review the possibilities of gammaray emission and prospects for GLAST observations. We also present a toy model of the non-thermal electron spectra that are produced by the acceleration mechanisms discussed in an accompanying paper.

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Section: Introductionsupporting

confidence: 78%

Section: Hard X-ray and Radio Emissionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonthermal Radiation Mechanisms

2008

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“…To investigate possible selection effects, we show in Fig cluster (A1656), not visible with the VLA at 1.4 GHz, and studied at this frequency by Kim et al (1990) combining VLA and DRAO data; A2319 observed by Feretti et al (1997) with the WSRT; A754 visible in VLA images because of the elongated and irregular structure of the radio halo.…”

Section: Halo Properties and Redshiftmentioning

confidence: 99%

Radio halos in nearby (z < 0.4) clusters of galaxies

Giovannini

Bonafede

Feretti

et al. 2009

A&A

170

263

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Context. The intra-cluster medium is characterized by thermal emission, and by the presence of large scale magnetic fields. In some clusters of galaxies, a diffuse non-thermal emission is also present, located at the cluster center and called radio halo. These sources indicate the existence of relativistic particles and magnetic fields in the cluster volume. Aims. In this paper we collect data on all known nearby cluster radio halos (z < 0.4), to discuss their statistical properties and to investigate their origin. Methods. We searched for published data on radio halos and reduced new and archive VLA data to increase the number of known radio halos.Results. We present data on 31 radio halos, 1 new relic source, and 1 giant filament. We note the discovery of a small size diffuse radio emission in a cluster (A1213) with very low X-ray luminosity. Among the statistical results, we confirm the correlation between the average halo radio spectral index and the cluster temperature. We also discuss the high percentage of clusters where both a relic and a radio halo is present. Conclusions. The sample of radio halos discussed here represents the population of radio halos observable with current radio telescopes. A new telescope generation is necessary for a more detailed multifrequency study, and to investigate the possible existence of a population of radio halos with different properties.

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“…Lawler & Dennison 1982; Appendix is only available in electronic form at http://www.aanda.org Vallée et al 1986;Kim et al 1990Kim et al , 1991Clarke et al 2001) and individual galaxy clusters and galaxy groups by analyzing detailed high resolution RM images (e.g. Perley & Taylor 1991;Taylor & Perley 1993;Feretti et al 1995Feretti et al , 1999aGovoni et al 2001;Taylor et al 2001;Eilek & Owen 2002;Govoni et al 2006;Taylor et al 2007;Guidetti et al 2008;Laing et al 2008;Guidetti et al 2010;Bonafede et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Rotation measures of radio sources in hot galaxy clusters

Govoni

Dolag

Murgia

et al. 2010

A&A

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Aims. The goal of this work is to investigate the Faraday rotation measure (RM) of radio galaxies in hot galaxy clusters in order to establish a possible connection between the magnetic field strength and the gas temperature of the intracluster medium. Methods. We performed Very Large Array observations at 3.6 cm and 6 cm of two radio galaxies located in A401 and Ophiuchus, a radio galaxy in A2142, and a radio galaxy located in the background of A2065. All these galaxy clusters are characterized by high temperatures. Results. We obtained detailed RM images at an angular resolution of 3 for most of the observed radio galaxies. The RM images are patchy and reveal fine substructures of a few kpc in size. Under the assumption that the radio galaxies themselves have no effect on the measured RMs, these structures indicate that the intracluster magnetic fields fluctuate down to such small scales. These new data are compared with RM information present in the literature for cooler galaxy clusters. For a fixed projected distance from the cluster center, clusters with higher temperature show a higher dispersion of the RM distributions (σ RM ), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (S X ) at the radio galaxy location and σ RM is confirmed, a possible connection between the σ RM − S X relation and the cluster temperature, if present, is very weak. Therefore, in view of the current data, it is impossible to establish a strict link between the magnetic field strength and the gas temperature of the intracluster medium.

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The halo and magnetic field of the Coma cluster of galaxies

Cited by 255 publications

References 0 publications

Nonthermal Radiation Mechanisms

Nonthermal Radiation Mechanisms

Radio halos in nearby (z < 0.4) clusters of galaxies

Rotation measures of radio sources in hot galaxy clusters

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