The merging galaxy cluster Abell 3266 at low radio frequencies

TL;DR

This study uses new low-frequency radio observations to explore the complex merging galaxy cluster Abell 3266, detecting multiple steep-spectrum sources, including relics and fossil plasma, but no giant radio halo, challenging existing scaling relations.

Contribution

It provides the highest-resolution low-frequency radio imaging of Abell 3266 and reports new detections of steep-spectrum sources, including a relic and fossil plasma, with upper limits on halo emission.

Findings

Detection of a 570 kpc radio relic and a possible connecting bridge.

Identification of two ultra-steep-spectrum fossil plasma sources.

Non-detection of a giant radio halo, with upper limits below expected levels.

Abstract

We present new low-frequency ($\nu = 88$-216 MHz) observations of the complex merging galaxy cluster Abell 3266. These new observations are taken with the Murchison Widefield Array (MWA) in its Phase II 'extended', long-baseline configuration, offering the highest-resolution low-frequency view of the cluster to date. We report on the detection of four steep spectrum ($\alpha \lesssim -1$ for $S_\nu \propto \nu^\alpha$) extended radio sources within the cluster. We confirm the detection of a $\sim 570$ kpc radio relic to the south of the cluster, and a possible bridge of emission connecting the relic to the cluster core. We also detect two new ultra-steep-spectrum ($\alpha \lesssim -1.7$) fossil plasma sources to the north and west of the cluster centre without associated compact radio emission. A previously detected radio galaxy in the cluster is also found to have a spectrally steepening tail with steep-spectrum components highlighted by the MWA. We do not detect a giant radio halo in the cluster. After simulating a range of radio haloes at 216 MHz we place upper limits on the radio luminosity corresponding to $\sim 7.2 \times 10^{24}$ W Hz$^{-1}$ at 150 MHz assuming the expected 500 kpc radius, up to a factor 5 lower than expected from scaling relations. Why a giant radio halo is undetected in Abell 3266 is unclear - the timeline of the merger and overall mass of the system as determined by optical and X-ray studies suggest the foundation for a hosting system.