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Andernach et al. report the results of a visual inspection of images
of the Rapid ASKAP Continuum Survey (RACS) in search of extended radio
galaxies (ERG) that exceed linear sizes on the order of one
Megaparsec (over three million light-years).
They searched an area of 1059 square degrees, which is covered by deep
multi-band optical images of the Dark Energy Survey (DES),
and increased the sample of known giant radio sourvces (GRS) by ∼39% to 636.
Why are giant radio sources so big? While factors including
(i) a preferred orientation in the plane of the sky, (ii) a location in lower-density environments, and (iii)
more powerful jets feeding their lobes all contribute, they cannot explain the observations
and it has been proposed that a key factor may be a much longer duration of their radio active phase.
The two largest GRS in the sample: the GRG J0054–4952 (projected linear size of 3.4 Mpc), and the GRQ J0500–4242
(projected linear size of 2.9 Mpc), overlaid on a composite of optical images from DES DR1.
The green contours from RACS and the gapped red crosses at centre mark the location of the hosts.
The insets show a zoom of an area of 1 arcminute × 1 arcminute
around the hosts. The left panel shows additional contours from the MWA GLEAM survey
in the 170-–231 MHz band, which delineate the outer lobes.
In the right panel the lobes are indicated with white arrows.
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