Astronomy & Astrophysics manuscript no. aanda
February 14, 2022
The discovery of a radio galaxy of at least 5 Mpc
Martijn S.S.L. Oei1?, Reinout J. van Weeren1, Martin J. Hardcastle2, Andrea Botteon1, Tim W. Shimwell1, Pratik
Dabhade3, Aivin R.D.J.G.I.B. Gast4, Huub J.A. Röttgering1, Marcus Brüggen5, Cyril Tasse6, 7, Wendy L. Williams1, and
1 Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2300 RA Leiden, The Netherlands
2 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hateld AL10 9AB, United Kingdom
3 Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France
4 Somerville College, University of Oxford, Woodstock Road, Oxford OX2 6HD, United Kingdom
5 Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
6 GEPI & USN, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
7 Department of Physics & Electronics, Rhodes University, PO Box 94, Grahamstown, 6140, South Africa
February 14, 2022
Context. Giant radio galaxies (GRGs, or colloquially ‘giants’) are the Universe’s largest structures generated by individual galaxies.
They comprise synchrotron-radiating AGN ejecta and attain cosmological (Mpc-scale) lengths. However, the main mechanisms that
drive their exceptional growth remain poorly understood.
Aims. To deduce the main mechanisms that drive a phenomenon, it is usually instructive to study extreme examples. If there exist
host galaxy characteristics that are an important cause for GRG growth, then the hosts of the largest GRGs are likely to possess
them. Similarly, if there exist particular large-scale environments that are highly conducive to GRG growth, then the largest GRGs
are likely to reside in them. For these reasons, we aim to perform a case study of the largest GRG available.
Methods. We reprocessed the LOFAR Two-metre Sky Survey (LoTSS) DR2 by subtracting compact source