Diffuse Radio Emission from Galaxy Clusters

Weeren, R. J. van; Gasperin, F. de; Akamatsu, Hiroki; Brüggen, M.; Feretti, L.; Kang, Hyesung; Stroe, Andra; Zandanel, F.

doi:10.1007/s11214-019-0584-z

Cited by 452 publications

(464 citation statements)

References 516 publications

(489 reference statements)

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“…2). Second, the low-efficiency issue of diffuse shock acceleration (DSA) in merger shocks is not a problem for the MA-shocks any more (see van Weeren et al 2019, and references therein). The MA-shocks' Mach number could reach a few tens to hundreds depending on the pre-heating process of the IGM.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Encounters of merger and accretion shocks in galaxy clusters and their effects on intracluster medium

Zhang

Churazov

Dolag

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Several types/classes of shocks naturally arise during formation and evolution of galaxy clusters. One such class is represented by accretion shocks, associated with deceleration of infalling baryons. Such shocks, characterized by a very high Mach number, are present even in 1D models of cluster evolution. Another class is composed of "runaway merger shocks", which appear when a merger shock, driven by a sufficiently massive infalling subcluster, propagates away from the main-cluster center. We argue that, when the merger shock overtakes the accretion shock, a new long-living shock is formed that propagates to large distances from the main cluster (well beyond its virial radius) affecting the cold gas around the cluster. We refer to these structures as Merger-accelerated Accretion shocks (MA-shocks) in this paper.We show examples of such MA-shocks in 1D and 3D simulations and discuss their characteristic properties. In particular, (1) MA-shocks shape the boundary separating the hot intracluster medium (ICM) from the unshocked gas, giving this boundary a "flower-like" morphology. In 3D, MA-shocks occupy space between the dense accreting filaments.(2) Evolution of MA-shocks highly depends on the Mach number of the runaway merger shock and the mass accretion rate parameter of the cluster. (3) MA-shocks may lead to the misalignment of the ICM boundary and the splashback radius.(racc rsp) if the gas adiabatic index is γ = 5/3 (see e.g. Shi 2016b) 1 .However, the evolution of galaxy clusters is more complicated than those one-dimensional (1D) self-similar solutions. Two major processes tend to break the self-similarity (and also spherical symmetry) of galaxy clusters, i.e. active galactic nucleus (AGN) feedback (see e.g. Werner et al. 2019, for a recent review) and cluster mergers (e.g. Sarazin 2002). The former process perturbs the gas in cluster cores (e.g. 100 kpc); the latter one, 1 Specifically, the alignment of the racc and rsp holds when γ = 5/3 only if the cluster mass accretion rate parameter (Γ) is in the range of 0.5 ≤ Γ ≤ 5 (Shi 2016b; see the definition of Γ in Section 2).

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Section: Conclusion and Discussionmentioning

confidence: 99%

Encounters of merger and accretion shocks in galaxy clusters and their effects on intracluster medium

Zhang

Churazov

Dolag

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The magnetic field is another great uncertainty in calculating the radio power from radio relics. Historically, most observations of radio relics suggest fairly high fields of 2-7 µG, also based on the lack of detection in the associated Inverse Compton emission from the same region, under simplistic assumptions (van Weeren et al 2019;Finoguenov et al 2010;Nakazawa et al 2009). More recently, the width of the radio relics has been used to constrain the magnetic field strength in the relic.…”

Section: Magnetic Fieldmentioning

confidence: 99%

Analytical model for cluster radio relics

Brüggen

Vazza

2020

Monthly Notices of the Royal Astronomical Society

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Radio relics are vast synchrotron sources that sit on the outskirts of merging galaxy clusters. In this work we model their formation using a Press-Schechter formalism to simulate merger rates, analytical models for the intracluster medium and the shock dynamics, as well as a simple model for the cosmic-ray electrons at the merger shocks. We show that the statistical properties of the population of radio relics are strongly dependent on key physical parameters, such as the acceleration efficiency, the magnetic field strength at the relic, the geometry of the relic and the duration of the electron acceleration at merger shocks. It turns out that the flux distribution as well as the power-mass relation can constrain key parameters of the intracluster medium. With the advent of new large-area radio surveys, statistical analyses of radio relics will complement what we have learned from observations of individual objects.

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“…However, lack of gamma ray detection puts constraints on such a mechanism (e.g., Brunetti et al 2017 and references therein). Apart from radio halos, diffuse radio sources in clusters can broadly be divided into radio relics (e.g., Kempner et al 2004;van Weeren et al 2019) and radio phoenices (revived fossil plasma sources). Cluster radio relics are elongated linearly polarized (>10%-30% at GHz frequencies) regions (∼ 1-2 Mpc) at the cluster outskirts, which typically have a convex morphology with respect to the cluster centre and exhibit a radio spectral steepening towards the cluster centre (van Weeren et al 2010;Bonafede et al 2012;Stroe et al 2013;de Gasperin et al 2015;Kierdorf et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Revived fossil plasma sources in galaxy clusters

Mandal

Intema

Weeren

et al. 2020

A&A

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It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intra-cluster medium by radio galaxies. These synchrotron-emitting electrons are very difficult to study, as their radiative life time is only tens of Myrs at GHz frequencies, and are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below a GHz. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-GHz frequencies, creating so-called radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper, we demonstrate the discovery potential of low frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TGSS and 1.4 GHz NVSS sky surveys to identify candidate radio phoenices. A subset of three candidates were studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray (Chandra or XMM-Newton) and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and helps to understand the physical origin of these sources.

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Diffuse Radio Emission from Galaxy Clusters

Cited by 452 publications

References 516 publications

Encounters of merger and accretion shocks in galaxy clusters and their effects on intracluster medium

Encounters of merger and accretion shocks in galaxy clusters and their effects on intracluster medium

Analytical model for cluster radio relics

Revived fossil plasma sources in galaxy clusters

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