Discovery of Rare Dying Radio Galaxies Using MeerKAT

Nadeem Oozeer,Michael F Bietenholz,Nceba Mhlahlo,Kenda Knowles,Lawrence Rudnick,Konstantinos Kolokythas,Tiziana Venturi

doi:10.3390/galaxies9040102

Abstract

Dying radio galaxies represent a stage of the evolution of active galactic nuclei (AGN), during which the accreting central black hole has switched off and/or falls to such a low level that the plasma outflow can no longer be sustained. When this happens, the radio source undergoes a period of fading, the dying phase, before it disappears completely. We present the study of three potential dying radio sources using the MeerKAT radio telescope: MKT J072851.2-752743, MKT J001940.4-654722, and ACO 548B. The identification as dying radio sources came from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). We carry out a multi-wavelength analysis of the sources and derive their energetics. The ages of the sources are ∼30–70 Myr, they have magnetic fields of the order of a few μG, and they have relatively low radio power. Their potential optical counterparts are associated with massive galaxies. We show that ACO 548B, previously classified as two peripheral relic radio sources, is a dying radio galaxy. With its good sensitivity and resolution, MeerKAT is an ideal instrument to detect potential dying radio sources, and contribute to the understanding of the evolution of AGN population.

Highlights

Extra-galactic radio sources play an essential role in areas ranging from the nature of active galactic nuclei (AGNs) and the environment of galaxies to those related to cosmology
We analysed three sources detected from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS) images
The most intriguing is ACO 548B, which had earlier been classified as two-relic system. We showed that this source is instead a dying radio galaxy due to the lack of hot intracluster medium (ICM), which would show up in X-ray emission, the non-peripheral location near the centre of the cluster, non-elongated radio morphology, and having energetics characteristic of dying radio sources

Summary

Introduction

Extra-galactic radio sources play an essential role in areas ranging from the nature of active galactic nuclei (AGNs) and the environment of galaxies to those related to cosmology. AGNs shine over a wide range of the electromagnetic spectrum, from radio to gamma rays. In almost all of this huge energy range, AGNs are the most luminous sources in the sky. It is well proven that some radio galaxies possess highly collimated and relativistic twin jets of matter that emerge from an AGN. The expansion of these jets produces a variety of morphologies. See [1] for a review

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