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11th of August 2021
A Giant Radio Galaxy
by Norris et al.
Norris et al. have recent published results from the Evolutionary Map of the Universe (EMU) Pilot Survey with the ASKAP telescope. The survey covers 270 square degreees of an area covered by the optical Dark Energy Survey (DES), resulting in a catalogue of ∼220,000 sources, the large majority of which are single-component sources. However, ASKAP provides a high sensitivity to low surface-brightness (faint and extended) emission, which results in the detection of types of sources that were rarely seen in previous surveys. An example is the class of Giant Radio Galaxies, which are Radio Galaxies (RGs) with a projected linear size was greater than 0.7 Mpc (2.3 million light years). They are rare -- only a few hundred have been catalogued -- and must be relatively old for the galaxy to have "grown" to such large dimensions. The image on the left above shows the Giant Radio Galaxy EMU PS J205139.8–570434, with radio shown in greyscale, overlaid on the DES DR1 colour image. (The horizontal and vertical green stripes are artefacts from combining DES survey images.) The Giant Radio Galaxy consists of the roughly north-south jet and the two diffuse plumes above and below it. The strong source to the east (left), surrounded by diffraction rings, is the well-studied galaxy IC 5063. The image on the right shows a contour diagram of the central part of the Giant Radio Galaxy at 18 arcsec resolution, overlaid on the DES DR1 colour image. Contour levels are 3, 7, 12 and 18 mJy/beam. The central region of the new Giant Radio Galaxy has been catalogued previously, however, the full extended structure had not been previously detected, ASKAP allows the radio emission to be traced over a Largest Angular Size of ∼22.1 arcmin, which at the distance of the source corresponds to a linear projected size of 1.53 Mpc (5 million light years). The galaxy's radio jets are oriented roughly North-South, feature several wiggles, and terminate in diffuse lobes at both extremes of the source.

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