The galaxy group NGC 507: Newly detected AGN remnant plasma transported by sloshing^⋆

¹ Dipartimento di Fisica e Astronomia, Universitá di Bologna, via P. Gobetti 93/2, 40129 Bologna, Italy
² INAF – Istituto di Radioastronomia, Bologna Via Gobetti 101, 40129 Bologna, Italy
e-mail: m.brienza@ira.inaf.it
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Piero Gobetti 93/3, 40129 Bologna, Italy
⁴ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁵ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF) – Milano, Via A. Corti 12, 20133 Milano, Italy
⁶ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁷ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁸ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁹ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
¹⁰ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
¹² SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
¹³ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583, Japan

Received: 3 November 2021
Accepted: 11 January 2022

Abstract

Jets from active galactic nuclei (AGN) are known to recurrently enrich their surrounding medium with mildly relativistic particles and magnetic fields. Here, we present a detailed multi-frequency analysis of the nearby (z = 0.01646) galaxy group NGC 507. In particular, we present new high-sensitivity and high-spatial-resolution radio images in the frequency range 144–675 MHz obtained using Low Frequency Array (LOFAR) and upgraded Giant Metrewave Radio Telescope (uGMRT) observations. These reveal the presence of previously undetected diffuse radio emission with complex, filamentary morphology likely related to a previous outburst of the central galaxy. Based on spectral ageing considerations, we find that the plasma was first injected by the AGN 240–380 Myr ago and is now cooling. Our analysis of deep archival X-ray Multi-Mirror Mission (XMM-Newton) data confirms that the system is dynamically disturbed, as previously suggested. We detect two discontinuities in the X-ray surface-brightness distribution (towards the east and south) tracing a spiral pattern, which we interpret as cold fronts produced by sloshing motions. The remarkable spatial coincidence observed between the newly detected arc-like radio filament and the southern concave X-ray discontinuity strongly suggests that the remnant plasma has been displaced by the sloshing motions on large scales. Overall, NGC 507 represents one of the clearest examples known to date in which a direct interaction between old AGN remnant plasma and the external medium is observed in a galaxy group. Our results are consistent with simulations that suggest that filamentary emission can be created by the cluster or group weather, disrupting AGN lobes and spreading their relativistic content into the surrounding medium.