Magnetic properties of the Abell 3391-3395 system revealed using wide-field MeerKAT polarimetry

TL;DR

This study uses MeerKAT polarimetry to map magnetic fields in the Abell 3391-3395 galaxy cluster system, revealing insights into intercluster magnetization through Faraday rotation measures.

Contribution

First detailed RM grid analysis of the Abell 3391-3395 system, demonstrating magnetic field properties in the intercluster environment with high sensitivity and resolution.

Findings

Clusters show increased RM scatter indicating stronger magnetic fields.

The bridge exhibits low RM scatter, suggesting a relatively ordered magnetic field.

No diffuse synchrotron emission detected, setting new upper limits on emissivity.

Abstract

Magnetic fields in cluster outskirts and the intercluster medium are poorly constrained because diffuse synchrotron emission is hard to detect at low surface brightness. Faraday rotation measures (RMs) of polarized background sources can probe foreground large-scale structure. The nearby interacting Abell 3391-3395 system hosts a well-established X-ray bridge, making it an excellent target for studying magnetization in the intercluster environment. We characterize the magnetized environment of Abell 3391/95 and its surroundings by constructing a dense RM grid from wide-field polarimetry. We observed Abell 3391/95 with MeerKAT in full polarization using a three-pointing mosaic. The data were calibrated with direction-independent and direction-dependent techniques and imaged using visibility-plane mosaicing for a large field of view at high sensitivity. Using Faraday synthesis, we formed Faraday cubes and measured RMs for polarized background sources. We defined on- and off-target regions using contours from a wavelet-filtered eROSITA image. We identified 434 polarized sources within the field, with a polarized source density ranging from about 30 sources per square degree in the outer regions to about 110 sources per square degree in the central field, and a field-averaged density of 73 sources per square degree. The clusters show a statistically significant enhancement of RM scatter relative to the off-target region. In contrast, the bridge shows comparatively low RM scatter, while an RM structure-function analysis on matched angular scales yields a tentative indication of larger RM differences in the bridge than off-target. Combined with low per-source depolarization, this suggests a bridge magnetic field relatively ordered on ~10 kpc scales, but less ordered on larger scales. The non-detection of diffuse synchrotron emission in the bridge yields improved upper limits on the emissivity.