Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA
Diego, J. M.; Tasse, C.; Eckert, D.; Botteon, A.; Bonafede, A.; Riseley, C. J.; Hopkins, A. M.; Carretti, E.; Collier, J. D.; Koribalski, B. S.; Reiprich, T. H.; Johnston-Hollitt, M.; Hoeft, M.; Rajpurohit, K.; Brienza, M.; Rudnick, L.; Galvin, T. J.; Vernstrom, T.; Di Mascolo, L.; Bonnassieux, E.; Duchesne, S. W.; Chokshi, A.; Quici, B.; Keel, R. R.
Italy, Australia, United States, Netherlands, Germany, Switzerland, France, South Africa, Spain
Abstract
Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of Abell 3266 performed with the Australian Square Kilometre Array Pathfinder (0.8-1.1 GHz) and the Australia Telescope Compact Array (1.1-3.1 GHz). These deep observations provide new insights into recently reported diffuse non-thermal phenomena associated with the intracluster medium, including a 'wrong-way' relic, a fossil plasma source, and an as-yet unclassified central diffuse ridge, which we reveal comprises the brightest part of a large-scale radio halo detected here for the first time. The 'wrong-way' relic is highly atypical of its kind: it exhibits many classical signatures of a shock-related radio relic, while at the same time exhibiting strong spectral steepening. While radio relics are generally consistent with a quasi-stationary shock scenario, the 'wrong-way' relic is not. We study the spectral properties of the fossil plasma source; it exhibits an ultrasteep and highly curved radio spectrum, indicating an extremely aged electron population. The larger scale radio halo fills much of the cluster centre, and presents a strong connection between the thermal and non-thermal components of the intracluster medium, along with evidence of substructure. Whether the central diffuse ridge is simply a brighter component of the halo, or a mini-halo, remains an open question. Finally, we study the morphological and spectral properties of the multiple complex radio galaxies in this cluster in unprecedented detail, tracing their evolutionary history.