Using Radio Halos and Minihalos to Measure the Distributions of Magnetic Fields and Cosmic Rays in Galaxy Clusters

Keshet, Uri; Loeb, Abraham

doi:10.1088/0004-637x/722/1/737

Cited by 99 publications

(108 citation statements)

References 88 publications

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“…-The observed correlation of radio halo luminosity with X-ray luminosity (L ν − L X relation, see Fig. 1) of clusters with halos holds within these models for plausible magnetic field values and CRp acceleration efficiencies (Dolag & Enßlin 2000;Miniati et al 2001a;Pfrommer 2008;Keshet & Loeb 2010). -Also the correlation of radio halo surface brightness with X-ray surface brightness of clusters with halos holds roughly for sensible magnetic field profiles and CRp acceleration efficiencies.…”

Section: Hadronic Modelssupporting

confidence: 61%

“…Such a mechanism is easily realised in the re-acceleration model of halo formation, due to the short cooling time of the radio emitting electrons, which just cool away once turbulence is unable to maintain them. It is less easily realised in the hadronic model via magnetic field decay after turbulence as proposed by Kushnir et al (2009) and Keshet & Loeb (2010), since the turbulent decay takes about a Gyr and the magnetic field decay is relatively gentle (Subramanian et al 2006). In addition, this argument appears weak because μG strong magnetic fields are commonly observed in clusters without diffuse radio emission .…”

Section: Observational Propertiesmentioning

confidence: 99%

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Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Enßlin

Pfrommer

Miniati

et al. 2011

A&A

202

294

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We investigate the interplay of cosmic ray (CR) propagation and advection in galaxy clusters. Propagation in form of CR diffusion and streaming tends to drive the CR radial profiles towards being flat, with equal CR number density everywhere. Advection of CR by the turbulent gas motions tends to produce centrally enhanced profiles. We assume that the CR streaming velocity is of the order of the sound velocity. This is motivated by plasma physical arguments. The CR streaming is then usually larger than typical advection velocities and becomes comparable or lower than this only for periods with trans-and super-sonic cluster turbulence. As a consequence a bimodality of the CR spatial distribution results. Strongly turbulent, merging clusters should have a more centrally concentrated CR energy density profile with respect to relaxed ones with very subsonic turbulence. This translates into a bimodality of the expected diffuse radio and gamma-ray emission of clusters, since more centrally concentrated CR will find higher target densities for hadronic CR proton interactions, higher plasma wave energy densities for CR electron and proton re-acceleration, and stronger magnetic fields. Thus, the observed bimodality of cluster radio halos appears to be a natural consequence of the interplay of CR transport processes, independent of the model of radio halo formation, be it hadronic interactions of CR protons or re-acceleration of low-energy CR electrons. Energy dependence of the CR propagation should lead to spectral steepening of dying radio halos. Furthermore, we show that the interplay of CR diffusion with advection implies first order CR re-acceleration in the pressure-stratified atmospheres of galaxy clusters. Finally, we argue that CR streaming could be important in turbulent cool cores of galaxy clusters since it heats preferentially the central gas with highest cooling rate.

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Section: Hadronic Modelssupporting

confidence: 61%

Section: Observational Propertiesmentioning

confidence: 99%

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Enßlin

Pfrommer

Miniati

et al. 2011

A&A

202

294

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“…As a final remark, in this paper we focussed only on the case of Mpc-sized radio halos. In reality, smaller halos could be generated in dynamically disturbed and relaxed systems by several mechanisms, including turbulent reacceleration in sloshing cores and in the region of AGN-driven bubbles (Cassano et al 2008b;Mazzotta & Giacintucci 2008;ZuHone et al 2012), reconnection regions (Lazarian & Brunetti 2011) and hadronic collisions (Pfrommer & Enßlin 2004;Keshet & Loeb 2010). All these halos constitute an additional population of diffuse synchrotron source in galaxy cluster to investigate with future radio surveys.…”

Section: Model Simplificationsmentioning

confidence: 99%

Radio halos in future surveys in the radio continuum

Cassano

Brunetti

Norris

et al. 2012

A&A

103

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Aims. Giant radio halos are Mpc-scale synchrotron sources detected in a significant fraction of massive and merging galaxy clusters. The statistical properties of radio halos can be used to discriminate among various models for the origin of non-thermal particles in galaxy clusters. Therefore, theoretical predictions are important as new radio telescopes are about to begin to survey the sky at low and high frequencies with unprecedented sensitivity. Methods. We carry out Monte Carlo simulations to model the formation and evolution of radio halos in a cosmological framework and extend previous calculations based on the hypothesis of turbulent-acceleration. We adopt a phenomenological approach by assuming that radio halos are either generated in turbulent merging clusters, or are purely hadronic sources generated in more relaxed clusters, "off-state" halos.Results. The models predict that the luminosity function of radio halos at high radio luminosities is dominated by the contribution of halos generated in turbulent clusters. The generation of these halos becomes less efficient in less massive systems causing a flattening of the luminosity function at lower radio luminosities, as also pointed out in previous studies. However, we find that potentially this can be more than compensated for by the intervening contribution of "off-state" halos that dominate at lower radio luminosities. We derive the expected number of halos to explore the potential of the EMU+WODAN surveys that will be carried out with ASKAP and Aperitif, respectively, in the near future. By restricting to clusters at redshifts ≤0.6, we show that the planned EMU+WODAN surveys at 1.4 GHz have the potential to detect up to about 200 new radio halos, increasing their number by one order of magnitude. A fraction of these sources will be "off-state" halos that should be found at flux level f 1.4 ≤ 10 mJy, presently accessible only to deep pointed observations. We also explore the synergy between surveys at different radio frequencies, the Tier 1 LOFAR survey at 150 MHz and the EMU+WODAN surveys at 1.4 GHz. We predict a larger number of radio halos in the LOFAR survey due to the high LOFAR sensitivity, but also due to the existence of halos with very steep spectrum that glow up preferentially at lower frequencies. These halos are only predicted in the framework of turbulent re-acceleration models and should not have counterparts in the EMU+WODAN surveys, thus the combination of the two surveys will test theoretical models.

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“…Mazzotta & Giacintucci 2008;Giacintucci et al 2014b) suggests that turbulence may be reaccelerating electrons to produce the mini-haloes (Mazzotta & Giacintucci 2008;ZuHone et al 2013;Giacintucci et al 2014a). In addition, the secondary electron models similar to those for radio haloes have also been suggested as explaining the mini-haloes that indeed trace the region where the number density of thermal targets in proton-proton collisions is higher (Pfrommer & Enßlin 2004;Keshet & Loeb 2010;Zandanel et al 2014). Based on the role of turbulent motions in the ICM and the transport of cosmic rays, a potential evolutionary connection between mini-haloes and radio haloes has also been suggested (e.g.…”

Section: Introductionmentioning

confidence: 97%

The Extended GMRT Radio Halo Survey

Kale¹,

Venturi²,

Giacintucci³

et al. 2015

A&A

134

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The intra-cluster medium contains cosmic rays and magnetic fields that are manifested through the large scale synchrotron sources, termed radio haloes, relics, and mini-haloes. The Extended Giant Metrewave Radio Telescope (GMRT) Radio Halo Survey (EGRHS) is an extension of the GMRT Radio Halo Survey (GRHS) designed to search for radio haloes using GMRT 610/235 MHz observations. The GRHS and EGRHS consists of 64 clusters in the redshift range 0.2−0.4 that have an X-ray luminosity larger than 5 × 10 44 erg s −1 in the 0.1−2.4 keV band and declination, δ > −31 • in the REFLEX and eBCS X-ray cluster catalogues. In this second paper in the series, GMRT 610/235 MHz data on the last batch of 11 galaxy clusters and the statistical analysis of the full sample are presented. A new mini-halo in RX J2129.6+0005 and candidate diffuse sources in Z5247, A2552, and Z1953 have been discovered. A unique feature of this survey are the upper limits on the detections of 1 Mpc sized radio haloes; 4 new are presented here, making a total of 31 in the survey. Of the sample, 58 clusters with adequately sensitive radio information were used to obtain the most accurate occurrence fractions so far. The occurrence fractions of radio haloes, mini-haloes and relics in our sample are ∼22%, ∼16% and ∼5%, respectively. The P 1.4 GHz − L X diagrams for the radio haloes and mini-haloes are presented. The morphological estimators -centroid shift (w), concentration parameter (c), and power ratios (P 3 /P 0 ) derived from the Chandra X-ray images -are used as proxies for the dynamical states of the GRHS and EGRHS clusters. The clusters with radio haloes and mini-haloes occupy distinct quadrants in the c− w, c− P 3 /P 0 and w− P 3 /P 0 planes, corresponding to the more and less morphological disturbance, respectively. The non-detections span both the quadrants.Key words. galaxies: clusters: general -radio continuum: galaxies IntroductionThe intra-cluster medium (ICM) is the diffuse matter that pervades the space between the galaxies in galaxy clusters. It is dominated by hot (∼10 7 −10 8 K) thermal plasma that emits thermal Bremsstrahlung that is detectable in soft X-ray bands and is also responsible for the thermal Sunyaev-Zel'dovich (SZ) effect. It has been found that the ICM also contains magnetic fields (0.1−1 μG) and relativistic electrons (Lorentz factors 1000) distributed over the entire cluster volume. The most direct evidence of this are the cluster-wide diffuse synchrotron sources detected in radio bands (see Feretti et al. 2012;Brunetti & Jones 2014, for reviews). They occur in a variety of morphologies and sizes and are classified into three main types, namely, radio haloes, radio relics, and mini-haloes.Radio haloes (RHs) are Mpc-sized sources found in massive, merging galaxy clusters. They typically trace the morphology of the X-ray surface brightness, show negligible polarisation, and Appendices are available in electronic form at http://www.aanda.org have synchrotron spectral indices 1 , α ≥ 1. The emitting relativistic electro...

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Using Radio Halos and Minihalos to Measure the Distributions of Magnetic Fields and Cosmic Rays in Galaxy Clusters

Cited by 99 publications

References 88 publications

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Radio halos in future surveys in the radio continuum

The Extended GMRT Radio Halo Survey

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