A candle in the wind: a radio filament in the core of the A3562 galaxy cluster

TL;DR

This study reports the discovery of a faint, straight radio filament in galaxy cluster A3562, aligned with a cold front, and explores its possible origins involving galaxy motion, magnetic fields, and cosmic ray diffusion.

Contribution

It presents the first observation of a narrow radio filament in A3562 and proposes mechanisms for its formation related to cluster dynamics and magnetic field interactions.

Findings

Radio filament spans 200 kpc and aligns with X-ray cold front.

Spectral index of the filament is approximately -1.5.

A compact, unusually faint radio source is found at the BCG.

Abstract

Using a MeerKAT observation of the galaxy cluster A3562 (a member of the Shapley Supercluster), we have discovered a narrow, long and straight, very faint radio filament, which branches out at a straight angle from the tail of a radio galaxy located in projection near the core of the cluster. The radio filament spans 200 kpc and aligns with a sloshing cold front seen in the X-rays, staying inside the front in projection. The radio spectral index along the filament appears uniform (within large uncertainties) at $\alpha\simeq -1.5$. We propose that the radio galaxy is located outside the cold front, but dips its tail under the front. The tangential wind that blows there may stretch the radio plasma from the radio galaxy into a filamentary structure. Some reacceleration is needed in this scenario to maintain the radio spectrum uniform. Alternatively, the cosmic ray electrons from that spot in the tail can spread along the cluster magnetic field lines, straightened by that same tangential flow, via anomalously fast diffusion. Our radio filament can provide constraints on this process. We also uncover a compact radio source at the Brightest Cluster Galaxy (BCG) that is 2--3 orders of magnitude less luminous than those in typical cluster central galaxies -- probably an example of a BCG starved of accretion fuel by gas sloshing.