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

TL;DR

This study uses high-sensitivity radio observations to explore low-energy mass assembly events in the Shapley Supercluster, revealing new diffuse emissions and galaxy interactions across multiple scales, from supercluster to galactic.

Contribution

It presents the first GHz detection of intercluster diffuse emission connecting a cluster and a group, and provides detailed morphological and spectral analysis of various radio features in the supercluster.

Findings

Detection of low brightness intercluster diffuse emission on a 1 Mpc scale.

Identification of a ram pressure stripped radio tail in galaxy SOS 61086.

Confirmation of the ultra-steep spectrum radio halo in A 3562.

Abstract

The Shapley Supercluster ($\langle z \rangle\approx0.048$) contains several tens of gravitationally bound clusters and groups, making it it is an ideal subject for radio studies of cluster mergers. 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. We created total intensity images of the full region between A 3558 and A 3562, from $\sim 230$ to $\sim 1650$ MHz, using ASKAP, MeerKAT and the GMRT, with sensitivities ranging from $\sim 6$ to $\sim 100$ $\mu$Jy 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. We report the first GHz frequency detection of extremely low brightness intercluster diffuse emission on a $\sim 1$ Mpc scale connecting a cluster and a group, namely: A 3562 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 A 3558. Finally (4), we confirm the ultra-steep spectrum nature of the radio halo in A 3562. Our study strongly supports the scenario of a flyby of SC 1329-313 north of A 3562 into the supercluster core. [abridged...]