Volume 643, November 2020
|Number of page(s)||10|
|Section||Cosmology (including clusters of galaxies)|
|Published online||20 November 2020|
The great Kite in the sky: A LOFAR observation of the radio source in Abell 2626⋆
Dipartimento di Fisica e Astronomia, Università di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
2 INAF, Istituto di Radioastronomia di Bologna, via Gobetti 101, 40129 Bologna, Italy
3 ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
5 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
6 International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
7 SKA Organisation, Jodrell Bank Observatory, Macclesfield SK11 9DL, UK
8 Jodrell Bank Centre for Astrophysics, Department of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
9 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
Accepted: 23 September 2020
Context. The radio source at the center of the galaxy cluster Abell 2626, also known as the Kite, stands out for its unique morphology composed of four symmetric arcs. Previous studies have probed the properties of this source at different frequencies and its interplay with the surrounding thermal plasma, but the puzzle of its origin is still unsolved.
Aims. We use a new LOw-Frequency ARray (LOFAR) observation from the LOFAR Two-meter Sky Survey at 144 MHz to investigate the origin of the Kite.
Methods. We present a detailed analysis of the new radio data, which we combined with archival radio and X-ray observations. We produced a new, resolved spectral index map of the source with a resolution of 7″ and we studied the spatial correlation of radio and X-ray emission to investigate the interplay between thermal and nonthermal plasma.
Results. The new LOFAR data changed our view of the Kite because we discovered two steep-spectrum (α < −1.5) plumes of emission connected to the arcs. The spectral analysis shows, for the first time, a spatial trend of the spectrum along the arcs with evidence of curved synchrotron spectra and a spatial correlation with the X-ray surface brightness. On the basis of our results, we propose that the Kite was originally an X-shaped radio galaxy whose fossil radio plasma, after the end of the activity of the central active galactic nucleus, has been compressed as a consequence of motions of the thermal plasma encompassing the galaxy. The interplay between the compression and advection of the fossil plasma, with the restarting of the nuclear activity of the central galaxy, could have enhanced the radio emission of the fossil plasma producing the arcs of the Kite. We also present the first, low-frequency observation of a jellyfish galaxy in the same field, in which we detect extended, low-frequency emission without a counterpart at higher frequencies.
Key words: galaxies: clusters: individual: Abell 2626 / galaxies: individual: IC 5338 / galaxies: jets / radio continuum: galaxies / radiation mechanisms: non-thermal / methods: observational
The reduced images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/643/A172
© ESO 2020
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