June 17, 2024
1 Solar System Way, Planet Earth, USA

Hidden Giants – National Radio Astronomy Observatory

Giant radio galaxies (GRGs) are radio galaxies that have grown to megaparsec scales. The Milky Way is about 100,000 light years across, but GRGs span millions of light years. They are very rare and their apparent large size can make them difficult to detect. But Brianna Sampson, a student at the University of the West Indies, suspects there are many of these giants hidden in the radio sky.

One way GRGs can form is when a galaxy's powerful radio jets extend into a region of intergalactic space that is fairly empty. Therefore, double radio sources associated with active galactic nuclei (DRAGN) are a good place to start looking for these giant radio galaxies. To find GRG, Brianna started with the TIFR GMRT Sky Survey (TGSS). The Giant Meter Wave Radio Telescope (GMRT) is located in India and offers an excellent view of both the northern and southern sky, so TGSS covers almost the entire radio sky.

A confirmed GRG as seen in FIRST (left) and TGSS (right).

Using an algorithm known as DRAGNhunter, Brianna identified more than 1,400 potential GRGs. But this is where things get a little complicated. Although TGSS covers almost the entire sky, its resolution is relatively low. Too low to confirm whether Brianna's potential GRGs are actually giant radio galaxies. So Brianna examined 30 of the potential GRGs that are also found in the Very Large Array's faint eight-inch radio sky (FIRST) images. Completed in 2011, the FIRST survey only covered about 25% of the sky, but did so at a much higher resolution than the TGSS.

Of the 30 potential GRGs found in both studies, Brianna was able to confirm that 27 of them were true Giant Radio Galaxies in the FIRST data. If this relationship holds overall, then there could be more than a thousand GRGs in the TGSS data. Future sky surveys at higher resolution will be needed to confirm these GRGs, but it is clear that the TIFR GMRT Sky Survey data contains hidden giants.

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