Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Domínguez-Fernández, Paola; Brüggen, M.; Vazza, Franco; Banda-Barragán, Wladimir; Rajpurohit, K.; Mignone, A.; Mukherjee, Dipanjan; Vaidya, Bhargav

doi:10.1093/mnras/staa3018

Cited by 44 publications

(60 citation statements)

References 74 publications

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“…A difference in Mach number may also arise from the X-ray and radio emission preferentially tracing different shocks along a line of sight (see e.g. van Weeren et al, 2016; Rajpurohit et al, 2020, and references therein) or may arise due to turbulence near the shock front (Domínguez-Fernández et al, 2021).…”

Section: Resultsmentioning

confidence: 99%

MWA and ASKAP observations of atypical radio-halo-hosting galaxy clusters: Abell 141 and Abell 3404

Duchesne

Johnston‐Hollitt

Wilber

2021

Publ. Astron. Soc. Aust.

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We report on the detection of a giant radio halo in the cluster Abell 3404 as well as confirmation of the radio halo observed in Abell 141 (with linear extents $\sim\!770$ and $\sim\!850$ kpc, respectively). We use the Murchison Widefield Array, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to characterise the emission and intervening radio sources from $\sim100$ to 1 000 MHz; power law models are fit to the spectral energy distributions with spectral indices $\alpha_{88}^{1\,110} = -1.66 \pm 0.07$ and $\alpha_{88}^{943} = -1.06 \pm 0.09$ for the radio halos in Abell 3404 and Abell 141, respectively. We find strong correlation between radio and X-ray surface brightness for Abell 3404 but little correlation for Abell 141. We note that each cluster has an atypical morphology for a radio-halo-hosting cluster, with Abell 141 having been previously reported to be in a pre-merging state, and Abell 3404 is largely relaxed with only minor evidence for a disturbed morphology. We find that the radio halo powers are consistent with the current radio halo sample and $P_\nu$ –M scaling relations, but note that the radio halo in Abell 3404 is an ultra-steep–spectrum radio halo (USSRH) and, as with other USSRHs lies slightly below the best-fit $P_{1.4}$ –M relation. We find that an updated scaling relation is consistent with previous results and shifting the frequency to 150 MHz does not significantly alter the best-fit relations with a sample of 86 radio halos. We suggest that the USSRH halo in Abell 3404 represents the faint class of radio halos that will be found in clusters undergoing weak mergers.

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Section: Resultsmentioning

confidence: 99%

MWA and ASKAP observations of atypical radio-halo-hosting galaxy clusters: Abell 141 and Abell 3404

Duchesne

Johnston‐Hollitt

Wilber

2021

Publ. Astron. Soc. Aust.

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“…This would be a possible scenario for the observed relic. Recently, Domínguez-Fernández et al (2020) studied the impact of shocks on the magnetic power spectrum. This study used MHD simulations of Mach number 2-3 shocks propagating through a turbulent ICM 200 3 kpc 3 box.…”

Section: Discussionmentioning

confidence: 99%

The intracluster magnetic field in the double relic galaxy cluster Abell 2345

Stuardi

Bonafede

Lovisari

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Magnetic fields are ubiquitous in galaxy clusters, yet their radial profile, power spectrum, and connection to host cluster properties are poorly known. Merging galaxy clusters hosting diffuse polarized emission in the form of radio relics offer a unique possibility to study the magnetic fields in these complex systems. In this paper, we investigate the intra-cluster magnetic field in Abell 2345. This cluster hosts two radio relics that we detected in polarization with 1-2 GHz JVLA observations. X-ray XMM-Newton images show a very disturbed morphology. We derived the Rotation Measure (RM) of five polarized sources within ∼1 Mpc from the cluster center applying the RM synthesis. Both, the average RM and the RM dispersion radial profiles probe the presence of intra-cluster magnetic fields. Using the thermal electron density profile derived from X-ray analysis and simulating a 3D magnetic field with fluctuations following a power spectrum derived from magneto-hydrodynamical cosmological simulations, we build mock RM images of the cluster. We constrained the magnetic field profile in the eastern radio relic sector by comparing simulated and observed RM images. We find that, within the framework of our model, the data require a magnetic field scaling with thermal electron density as B(r)∝ne(r). The best model has a central magnetic field (within a 200 kpc radius) of 2.8±0.1 μG. The average magnetic field at the position of the eastern relic is ∼0.3 μG, a factor 2.7 lower than the equipartition estimate.

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“…The Mach number of shock fronts can be estimated either by radio observations based on the assumption of the diffusive shock acceleration (DSA) theory (e.g., Krymskii 1977;Bell 1978;Blandford & Ostriker 1978) or by X-ray observations based on the Rankine-Hugoniot condition (Landau & Lifshitz 1959). The Mach numbers estimated from radio observations are systematically higher than those based on X-ray observations (van Weeren et al 2019), which could be due to the projection effects (Hong et al 2015) or the propagation of shocks through a magnetized turbulent ICM (Dominguez-Fernandez et al 2021). Nevertheless, most of the merging shocks are in low Mach numbers (M 3), which challenge the acceleration efficiency of the current DSA theory.…”

Section: Introductionmentioning

confidence: 81%

Deep Chandra observations of merging galaxy cluster ZwCl 2341+0000

Zhang

Simionescu

Stuardi

et al. 2021

A&A

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Context. Knowledge of X-ray shock and radio relic connection in merging galaxy clusters has been greatly extended in terms of both observation and theory over the last decade. ZwCl 2341+0000 is a double-relic merging galaxy cluster; previous studies have shown that half of the southern relic is associated with an X-ray surface brightness discontinuity, while the other half not. The discontinuity was believed to be a shock front. Therefore, it is a mysterious case of an only partial shock-relic connection. Aims. By using the 206.5 ks deep Chandra observations, we aim to investigate the nature of the southern surface brightness discontinuity. Meanwhile, we aim to explore new morphological and thermodynamical features. Methods. We perform both imaging and spectroscopic analyses to investigate the morphological and thermodynamical properties of the cluster. In addition to the X-ray data, we utilize the GMRT 325 MHz image and JVLA 1.5 GHz and 3.0 GHz images to compute radio spectral index maps. Results. Surface brightness profile fitting and the temperature profile suggest that the previously reported southern surface brightness discontinuity is better described as a sharp change in slope or as a kink. This kink is likely contributed by the disrupted core of the southern subcluster. The radio spectral index maps show spectral flattening at the south-eastern edge of the southern relic, suggesting that the location of the shock front is 640 kpc away from the kink, where the X-ray emission is too faint to detect a surface brightness discontinuity. We update the radio shock Mach number to be ℳradio, S = 2.2 ± 0.1 and ℳradio, N = 2.4 ± 0.4 for the southern and northern radio relics based on the injection spectral indices. We also put a 3σ lower limit on the X-ray Mach number of the southern shock to be ℳX-ray, S > 1.6. Meanwhile, the deep observations reveal that the northern subcluster is in a perfect cone shape, with a ∼400 kpc linear cold front on each side. This type of conic subcluster has been predicted by simulations but is observed here for the first time. It represents a transition stage between a blunt-body cold front and a slingshot cold front. Strikingly, we found a 400 kpc long gas trail attached to the apex of the cone, which could be due to the gas stripping. In addition, an over-pressured hot region is found in the south-western flank of the cluster.

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Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Cited by 44 publications

References 74 publications

MWA and ASKAP observations of atypical radio-halo-hosting galaxy clusters: Abell 141 and Abell 3404

MWA and ASKAP observations of atypical radio-halo-hosting galaxy clusters: Abell 141 and Abell 3404

The intracluster magnetic field in the double relic galaxy cluster Abell 2345

Deep Chandra observations of merging galaxy cluster ZwCl 2341+0000

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