University of Hertfordshire

From the same journal

From the same journal

By the same authors


  • A. O. Clarke
  • G. Heald
  • T. Jarrett
  • J. D. Bray
  • T. M. Cantwell
  • A. M. M. Scaife
  • M. Brienza
  • A. Bonafede
  • R. P. Breton
  • J. W. Broderick
  • D. Carbone
  • J. H. Croston
  • J. S. Farnes
  • J. J. Harwood
  • V. Heesen
  • A. Horneffer
  • A. J. van der Horst
  • M. Iacobelli
  • W. Jurusik
  • G. Kokotanekov
  • J. P. McKean
  • L. K. Morabito
  • D. D. Mulcahy
  • B. S. Nikiel-Wroczynski
  • E. Orru
  • R. Paladino
  • M. Pandey-Pommier
  • M. Pietka
  • R. Pizzo
  • L. Pratley
  • C. J. Riseley
  • H. J. A. Rottgering
  • A. Rowlinson
  • J. Sabater
  • K. Sendlinger
  • A. Shulevski
  • S. S. Sridhar
  • A. J. Stewart
  • C. Tasse
  • S. van Velzen
  • R. J. van Weeren
  • M. W. Wise
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Original languageEnglish
Article numberA25
Number of pages9
JournalAstronomy & Astrophysics
Journal publication date1 May 2017
Early online date24 Apr 2017
StatePublished - 1 May 2017


We report on the discovery in the LOFAR Multifrequency Snapshot Sky Survey (MSSS) of a giant radio galaxy (GRG) with a projected size of $2.56 \pm 0.07$ Mpc projected on the sky. It is associated with the galaxy triplet UGC 9555, within which one is identified as a broad-line galaxy in the Sloan Digital Sky Survey (SDSS) at a redshift of $0.05453 \pm 1 \times 10^{-5} $, and with a velocity dispersion of $215.86 \pm 6.34$ km/s. From archival radio observations we see that this galaxy hosts a compact flat-spectrum radio source, and we conclude that it is the active galactic nucleus (AGN) responsible for generating the radio lobes. The radio luminosity distribution of the jets, and the broad-line classification of the host AGN, indicate this GRG is orientated well out of the plane of the sky, making its physical size one of the largest known for any GRG. Analysis of the infrared data suggests that the host is a lenticular type galaxy with a large stellar mass ($\log~\mathrm{M}/\mathrm{M}_\odot = 11.56 \pm 0.12$), and a moderate star formation rate ($1.2 \pm 0.3~\mathrm{M}_\odot/\mathrm{year}$). Spatially smoothing the SDSS images shows the system around UGC 9555 to be significantly disturbed, with a prominent extension to the south-east. Overall, the evidence suggests this host galaxy has undergone one or more recent moderate merger events and is also experiencing tidal interactions with surrounding galaxies, which have caused the star formation and provided the supply of gas to trigger and fuel the Mpc-scale radio lobes.


This document is the Accepted Manuscript of an article accepted for publication in Astronomy & Astrophysics following peer review. The version of record [A. O. Clarke, et al, LOFAR MSSS: Discovery of a 2.56 Mpc giant radio galaxy associated with a disturbed galaxy group, A&A, Vol 601, May 2017), is available online at DOI Published by EDP Sciences. © ESO, 2017.

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