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arXiv · 2507.07549

The Peculiar Mini-Halo in the Shapley Supercluster Member Abell 3558

K. S. Trehaeven·T. Venturi·O. Smirnov·G. Di Gennaro·M. Rossetti·S. Giacintucci·S. Bardelli·P. Merluzzi·S. P. Sikhosana·D. Dallacasa·R. Kale·K. Knowles
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Abstract

We present a multi-band study of the diffuse emission in the galaxy cluster Abell 3558, located in the core of the Shapley Supercluster. Using new MeerKAT UHF-Band and uGMRT Band-3 observations, and published MeerKAT L-band and ASKAP 887 MHz data, we perform a detailed analysis of the diffuse emission in the cluster centre. We complement with XMM-Newton X-ray information for a thorough study of the connection between the thermal and non-thermal properties of the cluster. We find that the diffuse radio emission in the cluster centre is more extended than published earlier, with a previously undetected extension spanning 100 kpc towards the north beyond the innermost cold front, increasing the total size of the emission to 550 kpc, and shows a clear spatial correlation with the X-ray features. The overall radio spectrum is steep ($\alpha_{\rm 400\,MHz}^{\rm 1569\,MHz}=1.18\pm0.10$), with local fluctuations which show several connections with the X-ray surface brightness, cold fronts, and residual emission. The point-to-point correlation between the radio and X-ray surface brightness is sub-linear, and steepens with increasing frequency. We discuss the classification of the diffuse emission considering its overall properties, those of the ICM, and the existing scaling laws between the radio and X-ray quantities in galaxy clusters. We conclude that it is a mini-halo, powered by turbulent (re)-acceleration induced by sloshing motions within the cluster region delimited by the cold fronts, and it supports the picture of a known minor merger between A\,3558 and the group SC\,1327--312 with mass ratio 5:1.

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K. S. Trehaeven, T. Venturi, O. Smirnov, G. Di Gennaro, M. Rossetti, S. Giacintucci, S. Bardelli, P. Merluzzi, S. P. Sikhosana, D. Dallacasa, R. Kale, K. Knowles. 2025-07-10. The Peculiar Mini-Halo in the Shapley Supercluster Member Abell 3558. https://arxiv.org/abs/2507.07549

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