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Astronomers from the University of Wisconsin-Madison and elsewhere report the discovery of 63 new giant radio galaxies as part of the Faint Images of the Radio Sky at Twenty cm (FIRST) survey. The results are detailed in an article published on November 15 on the preprint server arXiv.
Giant radio galaxies (GRGs) are radio galaxies whose projected overall linear length exceeds at least 2.3 million light years. They are rare items grown in low density environments. In general, GRGs are important for astronomers to study the formation and evolution of radio sources.
Many GRGs are bilobed radio galaxies known as dual radio sources associated with active galactic nuclei (AGN) or DRAGN. They can be difficult to identify during radio surveys, because the lobes of radio galaxies can be detected as multiple sources. Therefore, many detectable GRGs may remain unidentified. FIRST, the use of the Very Large Array (VLA), due to its low frequency and good sensitivity to extended sources, has the potential to reveal the presence of many new GRGs.
That’s why a team of astronomers led by Soren Ramdhanie at the University of Wisconsin-Madison decided to analyze FIRST to look for previously undetected GRGs. They used the DRAGNhunter algorithm to identify double-lobe radio galaxies in the FIRST data and studied the new sources.
“DRAGNhunter identifies DRAGNs by matching cataloged extended radio sources based on their separation and relative alignment, then uses the likelihood ratio approach to search for the likely host galaxy in the AllWISE catalog,” the researchers explained.
As a result, Ramdhanie’s team initially identified 80 giant radio galaxies in the first dataset using the DRAGNhuster algorithm. It turns out that 17 of the GRGs detected are within 5 arcseconds of known galaxies of this type and do not constitute new discoveries.
The newly discovered GRGs were found at redshifts between 0.51 and 1.32. Only six galaxies in the sample have spectroscopic redshifts, while the other 57 have estimated photometric redshifts. The GRG with the highest redshift is designated DELS J225125.27−025451.8.
The largest GRG reported in the study was given the designation DELS J093016.68+114241.4. It has a projected linear size of almost 4 million light years and was found with a redshift of 1.14. The smallest, DELS J234027.85+003057.4 with a redshift of 1.01, has a projected linear size of 2.3 million light years.
The study also found that the new GRGs have 1.4 GHz brightnesses ranging from 25.34 to 27.09 W/Hz. The flux density of these galaxies is scattered and has been measured between 7.14 and 337.85 mJy.
Further studies on new GRGs are needed to better understand their properties. The astronomers added that some of these GRGs may have been identified as extended radio galaxies in previous catalogs.
More information:
Soren Ramdhanie et al, The discovery of 63 giant radio galaxies in the FIRST survey, arXiv (2023). DOI: 10.48550/arxiv.2311.09079
Journal information:
arXiv
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Quote: FIRST discovery of dozens of new giant radio galaxies (November 24, 2023) retrieved November 25, 2023 from
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