Radio footprints of a minor merger in the Shapley Supercluster: From supercluster down to galactic scales

¹ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
e-mail: tventuri@ira.inaf.it
² Naval Research Laboratory, 4555 Overlook Avenue SW, Code 7213, Washington, DC 20375, USA
³ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
⁴ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁵ Dipartimento di Fisica e Astronomia, Universita di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁶ Astrophysics Research Centre, University of KwaZulu-Natal, Durban 4041, South Africa
⁷ School of Mathematics, Statistics, and Computer Science, University of KwaZulu-Natal, Westville 3696, South Africa
⁸ NRAO, PO Box 0 Soccoro, NM 87801, USA
⁹ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
¹⁰ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa
¹¹ Universitá di Roma Tor Vergata, Via della Ricerca Scientifica, 00133 Roma, Italy
¹² IASF-Milano, INAF, Via A. Corti 12, 20133 Milano, Italy
¹³ Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA
¹⁴ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁵ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹⁶ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Ganeshkhind, Pune 411007, India
¹⁷ Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76 Epping, NSW 1710, Australia
¹⁸ Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
¹⁹ Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
²⁰ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
²¹ Australian Astronomical Optics, Macquarie University, 105 Delhi Rd, North Ryde, NSW 2113, Australia
²² Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
²³ GEPI & USN, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
²⁴ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown 6140, South Africa
²⁵ CSIRO Astronomy and Space Science, PO Box 1130 Bentley, WA 6102, Australia
²⁶ Instituto de Fisica de Cantabria, CSIC-Universidad de Cantabria, 39005 Santander, Spain

Received: 20 October 2021
Accepted: 9 December 2021

Abstract

Context. The Shapley Supercluster (⟨z⟩≈0.048) contains several tens of gravitationally bound clusters and groups, making it an ideal subject for radio studies of cluster mergers.

Aims. We used new high sensitivity radio observations to investigate the less energetic events of mass assembly in the Shapley Supercluster from supercluster down to galactic scales.

Methods. We created total intensity images of the full region between A3558 and A3562, from ∼230 to ∼1650 MHz, using ASKAP, MeerKAT and the GMRT, with sensitivities ranging from ∼6 to ∼100 μJy beam⁻¹. We performed a detailed morphological and spectral study of the extended emission features, complemented with ESO-VST optical imaging and X-ray data from XMM-Newton.

Results. We report the first GHz frequency detection of extremely low brightness intercluster diffuse emission on a ∼1 Mpc scale connecting a cluster and a group, namely: A3562 and the group SC 1329–313. It is morphologically similar to the X-ray emission in the region. We also found (1) a radio tail generated by ram pressure stripping in the galaxy SOS 61086 in SC 1329–313; (2) a head-tail radio galaxy, whose tail is broken and culminates in a misaligned bar; (3) ultrasteep diffuse emission at the centre of A3558. Finally (4), we confirm the ultra-steep spectrum nature of the radio halo in A3562.

Conclusions. Our study strongly supports the scenario of a flyby of SC 1329–313 north of A3562 into the supercluster core. This event perturbed the centre of A3562, leaving traces of this interaction in the form of turbulence between A3562 and SC 1329–313, at the origin of the radio bridge and eventually affecting the evolution of individual supercluster galaxies by triggering ram pressure stripping. Our work shows that minor mergers can be spectacular and have the potential to generate diffuse radio emission that carries important information on the formation of large-scale structures in the Universe.