The prototypical major cluster merger Abell 754

Astronomy and Astrophysics, vol. 690, pp. A222

Abstract

Context. Abell 754 is a rich galaxy cluster at z = 0.0543 and is considered the prototype of a major cluster merger. As many dynamically unrelaxed systems, it hosts diffuse radio emission on megaparsec-scales. Extended synchrotron sources in the intra-cluster medium (ICM) are commonly interpreted as evidence that a fraction of the gravitational energy released during cluster mergers is dissipated into nonthermal components. Aims. Here, we aim to use new MeerKAT UHF- and L-band observations to study nonthermal phenomena in Abell 754. These data are complemented with archival XMM-Newton observations to investigate the resolved spectral properties of both the radio and X-ray cluster emission. Methods. For the first time, we employed the pipeline originally developed to calibrate LOFAR data to MeerKAT observations. This allowed us to perform a direction-dependent calibration and obtain highly sensitive radio images in UHF and L bands that capture the extended emission with unprecedented detail. By using a large XMM-Newton mosaic, we produced thermodynamic maps of the ICM. Results. Our analysis reveals that the radio halo in the cluster center is bounded by the well-known shock in the eastern direction. Furthermore, in the southwest periphery, we discover an extended radio source that we classify as a radio relic that is possibly tracing a shock driven by the squeezed gas compressed by the merger, outflowing in perpendicular directions. The low-luminosity of this relic appears compatible with direct acceleration of thermal pool electrons. We interpret the observed radio and X-ray features in the context of a major cluster merger with a nonzero impact parameter. Conclusions. Abell 754 is a remarkable galaxy cluster showcasing exceptional features associated with the ongoing merger event. The high quality of the new MeerKAT data motivates further work on this system.

Authors 8

1. A. Botteon

   Istituto di Radioastronomia di Bologna · National Institute for Astrophysics

   Affiliation as printed

   INAF – IRA, via P. Gobetti 101, 40129 Bologna, Italy

2. Reinout J. van Weeren Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

3. D. Eckert

   University of Geneva

   Affiliation as printed

   Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland

4. F. Gastaldello

   National Institute for Astrophysics

   Affiliation as printed

   INAF – IASF Milano, via A. Corti 12, 20133 Milano, Italy

5. Maxim L. Markevitch

   Goddard Space Flight Center

   Affiliation as printed

   NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA

6. S. Giacintucci

   United States Naval Research Laboratory

   Affiliation as printed

   U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Code 7213, Washington, DC 20375, USA

7. G. Brunetti

   Istituto di Radioastronomia di Bologna · National Institute for Astrophysics

   Affiliation as printed

   INAF – IRA, via P. Gobetti 101, 40129 Bologna, Italy

8. Ruta Kale

   Tata Institute of Fundamental Research · National Centre for Radio Astrophysics

   Affiliation as printed

   National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University, Pune 411007, India