With the help of civilian scientists, astronomers have discovered five new giant radio galaxies (GRGs). The new GRGs range in size from 2.3 to 2.6 million light-years. This is reported in an article posted on the arXiv preprint server.
GRGs are radio galaxies with a total projected linear length exceeding 2.28 million light-years. These are rare objects that appeared in low-density conditions. Giant radio galaxies are important to astronomers in studying the formation and evolution of radio sources.
A team of astronomers led by Hongming Thang from the University of Manchester, UK, reports the discovery of five previously unknown GRGs. The discovery is based on data from the civilian science project Radio Galaxy Zoo (RGZ). The RGZ DR1 is a hand-collated catalog of radio galaxies created by over 12,000 civilian volunteer scientists.
“In this article, we present the identification of five previously unknown giant radio galaxies (GRGs) using the release of data from the first civilian science project Radio Galaxy Zoo and a selection method suitable for training and validating deep learning algorithms for new radio surveys,” the astronomers report.
The recently identified GRG groups are designated J0941 + 3126, J1331 + 2557, J1402 + 2442, J1421 + 1016, and J1646 + 3627. All of them have relatively high radio luminosities and are likely to be either elliptical or intermediate disk galaxies.
J1402 + 2442 (also known as B2 1400 + 24) is the largest recently discovered GRG. It has a redshift of approximately 0.337 and is hosted by a pair of nearby galaxies designated SDSS J140224.25 + 244224.3 and SDSS J140224.31 + 244226.8.
Redshift is a phenomenon in which electromagnetic radiation increases its wavelength (for example, the light becomes redder), respectively, its frequency and energy decreases.
In the case of J1646 + 3627, a galaxy at least 2.46 million light-years across, the researchers found that this object is also the brightest cluster galaxy (BCG) in the GMBCG J251.67741 +36.45295 galaxy cluster. This discovery prompted Tang’s team to further explore cluster galaxies. They report that 13 previously known giant radio galaxies can be classified as bright cluster galaxy candidates.
The other two giant radio galaxies described in the study, namely J1331 + 2357 and J1421 + 1016, are about 2.62 and 2.49 million light-years across, respectively.