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25th of February 2021
The remnant radio galaxy MIDAS J225607-343212
by Quici et al.
The extensive lobes of radio galaxies are powered by jets launched from the environment of the super-massive black hole at the core of the galaxy. During this active phase the core of the galaxy is often a bright, compact, flat-spectrum radio source. When these jets "switch off", the radio galaxy enters a remnant phase. Quici et al. have searched for radio galaxies in this phase by taking advantage of multi-frequency radio imaging of a sub-region of the GAMA 23 field. They examine data from the Murchison Wide-field Array (216 MHz), the Australia Square Kilometer Array Pathfinder (887 MHz), and the Australia Telescope Compact Array (5.5 GHz). Adopting an ‘absent radio core’ criterion, they identify 10 radio galaxies showing no evidence for an active nucleus and classify these as new candidate remnant radio galaxies.

The image above, of MIDAS J225607-343212 has a VIKING near-infrared image as the background. Three sets of contours are overlaid, representing the radio emission as seen by ASKAP (black), and ATCA 5.5 GHz (orange). Red markers are overlaid on the positions of potential host galaxies. This source has a pair of relaxed radio lobes, with a diffuse bridge of emission connecting the lobes along the jet axis. Along the projected centre of the jet axis, three potential host galaxies exist. All three have similar redshifts of ~0.3, and so estimates of the corresponding physical size and radio power can be made irrespective of which is the actual host. G1 appears to be the most likely host as it lies closest to the projected centre of the radio lobes. The two compact components above and below are expected to be unrelated to the remnant galaxy. The results have been published in Publications of the Astronomical Society of Australia.

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