Peculiar giant radio galaxy GRG-J223301+131502 studied by researchers

An international team of astronomers has made radio and optical observations of a peculiar giant radio galaxy known as GRG-J223301+131502. The results of the observing campaign shed more light on the properties of this galaxy and have revealed its extraordinary jet structure. The findings are published in a paper published on arXiv.org on September 26.

The so-called Giant Radio Galaxies (GRGs) are radio galaxies with a total projected linear length of at least 2.3 million light-years. They are rare objects that are bred in low-density environments. In general, GRGs are important for astronomers to study the formation and evolution of radio sources.

About a thousand GRGs have been discovered so far, of which only ten are larger than 10 million light-years. The largest is J1420-0545 – with a projected length of about 16 million light years. Therefore, GRGs, and also the rest of the megaparsec-sized radio galaxies, are believed to be the largest single-galactic phenomena in the Universe.

With a redshift of 0.093, GRG-J223301+131502 (GRG-J2233+1315 for short) is a giant radio galaxy first identified in 2017 as part of the Search and Analysis of GRGs with Associated Nuclei (SAGAN) project. It has a total projected linear size of almost 5.57 million light-years and is hosted by SDSSJ223301.30+131502.5 – an S0-a type galaxy that features a large diffuse stellar halo.

Previous studies of GRG-J2233+1315 have found this galaxy to reside in a dense cluster environment, in contrast to current theories that GRGs typically live in sparse environments. To verify this, a group of astronomers led by Pratik Dabhade of the Sorbonne University in Paris, France, performed deep multi-frequency radio observations of GRG-J2233+1315 using the Giant Metrewave Radio Telescope (GMRT) and low-frequency array (LOFAR) and spectroscopic observations with the William Herschel Telescope (WHT).

The deep and high-resolution radio images revealed a giant jet about 772,000 light-years across, emanating from the radio core of GRG-J2233+1315 and resulting in a ‘kink’ stretching about 326,000 light-years. The images also show that the galaxy has lobes with no prominent hotspots and is very similar to a barbell, so the researchers dubbed GRG-J2233+1315 Barbell GRG. These discovered lobes turned out to have a magnetic field strength of about 5 µG and a spectral age of between 110 and 200 million years.

The observations revealed that Barbell GRG has a redshift of about 0.99 and that its linear size is larger than previously thought – nearly 6 million light-years. The results suggest that the host galaxy has a relatively low star formation rate – at the level of about 0.001 solar masses per year.

The authors of the work summarized the results and underlined the importance of their results for future studies.

“The discovery of the ∼100 kpc ‘kink’ structure from our study provides a unique opportunity to test different MHDs [magnetohydrodynamic] Large-scale models….This GRG with two-sided, large-area jets with a kink and diffuse outerlobes located in a cluster environment offers the opportunity to study the structure and growth of GRGs in different environments,” the researchers said closed.

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