Rotation measure synthesis applied to synthetic SKA images of galaxy clusters

Loi, F.; Murgia, M.; Govoni, F.; Vacca, V.; Bonafede, A.; Ferrari, C.; Prandoni, I.; Feretti, L.; Giovannini, G.; Li, H.

doi:10.1093/mnras/stz2699

Cited by 17 publications

(16 citation statements)

References 45 publications

(45 reference statements)

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“…In this situation, since we are looking at the differences between filaments, L would represent a characteristic separation between filaments along the line of sight, which we have scaled to 100 kpc. We find a magnetic field strength B ∼ 0.15 µG, which is consistent with those of typical clusters modelled by Loi et al (2019) at ∼1 Mpc from their cores (see their Fig. 2).…”

Section: Rotation Measure Analysissupporting

confidence: 89%

MeerKAT view of the diffuse radio sources in Abell 3667 and their interactions with the thermal plasma

Gasperin

Rudnick

Finoguenov

et al. 2022

A&A

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Context. During their lifetimes, galaxy clusters grow through the accretion of matter from the filaments of the large-scale structure and from mergers with other clusters. These mergers release a large amount of energy into the intracluster medium (ICM) through merger shocks and turbulence. These phenomena are associated with the formation of radio sources known as radio relics and radio halos, respectively. Radio relics and halos are unique proxies for studying the complex properties of these dynamically active regions of clusters and the microphysics of the ICM more generally. Aims. Abell 3667 is a spectacular example of a merging system that hosts a large pair of radio relics. Due to its proximity (z = 0.0553) and large mass, the system enables the study of these sources to a uniquely high level of detail. However, being located at Dec = −56.8°, the cluster could only be observed with a limited number of radio facilities. Methods. We observed Abell 3667 with MeerKAT as part of the MeerKAT Galaxy Cluster Legacy Survey. We used these data to study the large-scale emission of the cluster, including its polarisation and spectral properties. The results were then compared with simulations. Results. We present the most detailed view of the radio relic system in Abell 3667 to date, with a resolution reaching 3 kpc. The relics are filled with a network of filaments with different spectral and polarisation properties that are likely associated with multiple regions of particle acceleration and local enhancements of the magnetic field. Conversely, the magnetic field in the space between filaments has strengths close to what would be expected in unperturbed regions at the same cluster-centric distance. Comparisons with magnetohydrodynamic cosmological and Lagrangian simulations support the idea of filaments as multiple acceleration sites. Our observations also confirm the presence of an elongated radio halo, developed in the wake of the bullet-like sub-cluster that merged from the south-east. Finally, we associate the process of magnetic draping with a thin polarised radio source surrounding the remnant of the bullet’s cool core. Conclusions. Our observations have unveiled the complexity of the interplay between the thermal and non-thermal components in the most active regions of a merging cluster. Both the intricate internal structure of radio relics and the direct detection of magnetic draping around the merging bullet are powerful examples of the non-trivial magnetic properties of the ICM. Thanks to its sensitivity to polarised radiation, MeerKAT will be transformational in the study of these complex phenomena.

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Section: Rotation Measure Analysissupporting

confidence: 89%

MeerKAT view of the diffuse radio sources in Abell 3667 and their interactions with the thermal plasma

Gasperin

Rudnick

Finoguenov

et al. 2022

A&A

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“…Filaments of diffuse emission have also been observed in the galaxy cluster A2255. Govoni et al (2005) classified them as peripheral structures associated with the radio halo in agreement with expectations from numerical simulations (Loi et al 2019), while Pizzo et al (2011) classified them as relics, due to their morphology, fractional polarization level and rotation measure. The filaments in A2255 show spectral indices flatter (𝛼 ∼ 0.8 − 1.3) than the rest of the diffuse emission (up to 𝛼 ∼ 2), see also Botteon et al (2020).…”

Section: Filamentssupporting

confidence: 68%

“…Moreover, a 5𝜎 upper limit of 13% on the fractional polarization has been derived for the radio halo in 1E 0657-55.8 by Shimwell et al (2014). Three-dimensional numerical simulations suggest that radio halos are intrinsically polarized at 1.4 GHz, with filaments of polarized emission expected to be observed at distances greater than 1.5 Mpc from the cluster center, reflecting the intracluster magnetic field structure (Loi et al 2019). However, the resolution and sensitivity of present instruments hinder the detection of this polarized emission in most radio halos (Govoni et al 2013).…”

mentioning

confidence: 98%

Spectral study of the diffuse synchrotron source in the galaxy cluster Abell 523

Vacca,

Shimwell,

Perley

et al. 2022

Preprint

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The galaxy cluster Abell 523 (A523) hosts an extended diffuse synchrotron source historically classified as a radio halo. Its radio power at 1.4 GHz makes it one of the most significant outliers in the scaling relations between observables derived from multi-wavelength observations of galaxy clusters: it has a morphology that is different and offset from the thermal gas, and it has polarized emission at 1.4 GHz typically difficult to observe for this class of sources. A magnetic field fluctuating on large spatial scales (∼1 Mpc) can explain these peculiarities but the formation mechanism for this source is not yet completely clear. To investigate its formation mechanism, we present new observations obtained with the LOw Frequency ARray at 120-168 MHz and the Jansky Very Large Array at 1-2 GHz, which allow us to study the spectral index distribution of this source. According to our data the source is observed to be more extended at 144 MHz than previously inferred at 1.4 GHz, with a total size of about 1.8 Mpc and a flux density 𝑆 144 MHz = (1.52 ± 0.31) Jy. The spectral index distribution of the source is patchy with an average spectral index 𝛼 ∼ 1.2 between 144 MHz and 1.410 GHz, while an integrated spectral index 𝛼 ∼ 2.1 has been obtained between 1.410 GHz and 1.782 GHz. A previously unseen patch of steep spectrum emission is clearly detected at 144 MHz in the south of the cluster. Overall, our findings suggest that we are observing an overlapping of different structures, powered by the turbulence associated with the primary and a possible secondary merger.

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“…This is primarily because detection of polarized signals from radio halos has so far proved to be an arduous task with current radio interferometers (Vacca et al 2010). More recent works (Govoni et al 2013(Govoni et al , 2015Loi et al 2019) explore the possibility of their detection with upcoming radio interferometers like the SKA and it's precursors. The issue is non-trivial to say the least as the observables themselves such as the synchrotron intensity (I sync ), the Stokes Q and U parameters are related to the components of the field in a non-linear manner.…”

Section: Discussionmentioning

confidence: 99%

Properties of polarized synchrotron emission from fluctuation-dynamo action -- I. Application to galaxy clusters

Sur,

Basu,

Subramanian

2020

Preprint

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Using magnetohydrodynamic simulations of fluctuation dynamos, we perform broadbandwidth synthetic observations to investigate the properties of polarized synchrotron emission and the role Faraday rotation plays in inferring the polarized structures in the intracluster medium (ICM) of galaxy clusters. In the saturated state of the dynamo, we find a Faraday depth (FD) dispersion σ FD ≈ 100 rad m −2 , in agreement with observed values in the ICM. Remarkably, the FD power spectrum is qualitatively similar to M(k)/k, where M(k) is the magnetic spectrum and k the wavenumber. However, this similarity is broken at high k when FD is obtained by applying RM synthesis to polarized emission from the ICM due to poor resolution and complexities of spectrum in FD space. Unlike the Gaussian probability distribution function (PDF) obtained for FD, the PDF of the synchrotron intensity is log-normal. Relatively large σ FD in the ICM gives rise to strong frequency-dependent variations of the pixel-wise mean and peak polarized intensities at low frequencies ( 1.5 GHz). The mean fractional polarization p obtained at the resolution of the simulations increases from < 0.1 at 0.5 GHz to its intrinsic value of ∼ 0.3 at 6 GHz. Beam smoothing significantly affects the polarization properties below 1.5 GHz, reducing p to ∼ 0.01 at 0.5 GHz. At frequencies 5 GHz, polarization remains largely unaffected, even when recovered using RM synthesis. Thus, our results underline the need for high frequency ( 5 GHz) observations with future radio telescopes to effectively probe the properties of polarized emission in the ICM.

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Rotation measure synthesis applied to synthetic SKA images of galaxy clusters

Cited by 17 publications

References 45 publications

MeerKAT view of the diffuse radio sources in Abell 3667 and their interactions with the thermal plasma

MeerKAT view of the diffuse radio sources in Abell 3667 and their interactions with the thermal plasma

Spectral study of the diffuse synchrotron source in the galaxy cluster Abell 523

Properties of polarized synchrotron emission from fluctuation-dynamo action -- I. Application to galaxy clusters

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