Fifteen new giant radio galaxies discovered with ASKAP

Using the Australian Square Kilometer Array Pathfinder (ASKAP), astronomers have discovered 15 new giant radio galaxies with physical sizes exceeding 3 million light years. The finding was reported in a research paper published April 9 on the arXiv preprint server.

The so-called giant radio galaxies (GRGs) have an overall projected linear length exceeding at least 2.3 million light years. They are rare objects grown usually in low-density environments and display jets and lobes of synchrotron-emitting plasma. GRGs are important for astronomers studying the formation and the evolution of radio sources.

ASKAP is a 36-dish radio-interferometer operating at 700 to 1,800 MHz. It uses novel technology to achieve extremely high survey speed, making it one of the best instruments in the world for mapping the sky at radio wavelengths. Due to its large field of view, high resolution, dynamic range and good sensitivity to low-surface brightness structures, ASKAP has been essential in the search for new GRGs.

Now, a team of astronomers led by Baerbel Silvia Koribalski of the Western Sydney University in Australia reports the detection of new GRGs with ASKAP.

“We present the discovery of 15 well-resolved giant radio galaxies with angular sizes ≥5 arcmin and physical sizes >1 Mpc in wide-field Phased Array Feed 944 MHz observations on the Australian Square Kilometer Array Pathfinder,” the researchers wrote in the paper.

The newfound GRGs have projected linear sizes between 3.7 and 12.36 million light years, and were identified at redshifts of 0.056–0.735. Two of them, designated ASKAP J0044–2317 and ASKAP J0059–2352, were classified as candidate GRGs as they require further observations to confirm their GRG status.

The astronomers noted that the newly detected GRGs showcase a wide range of morphologies, and eight of them turned out to be Fanaroff-Riley Class II (FR II) galaxies, which are characterized by prominent radio hot spots at the end of their radio lobes. Four of the new GRS were classified as Fanaroff-Riley Class I (FR I) galaxies as they have bright inner radio jets and fading outer radio lobes without hotspots. The remaining three GRGs appear to be intermediate FR I/II or hybrid galaxies.

The largest GRG in the sample is ASKAP J0107–2347 at a redshift of 0.31. It is an FR II-type galaxy double-double radio galaxy (DDRG) as it has two sets of double lobes. The authors of the paper noted that ASKAP J0107–2347 harbors newly formed inner lobes, which already span about 2 million light years and are bright and compact, while its outer relic lobes are elongated and have very low surface brightness.

© 2025 Science X Network