A new ring galaxy discovered by Indian astronomers

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Optical color composite image of galaxy DJ0240. Credit: Krishna et al., 2023.

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Optical color composite image of galaxy DJ0240. Credit: Krishna et al., 2023.

By analyzing data from the Dark Energy Camera Legacy Survey (DECaLS), astronomers from Christ University in Bangalore, India, serendipitously discovered a new ring galaxy, which has been designated DES J024008.08-551047.5 and may belong to a rare class of galaxies. . Polar ring galaxies. This finding was published in a research paper posted Aug. 29 on a preprint server arXiv.

The so-called polar ring galaxies (PRGs) are systems consisting of an S0-like galaxy and a polar ring, which remain separate for billions of years. In general, these outer polar rings, made up of gas and stars, line up roughly in a perpendicular direction with respect to the main axis of the central host galaxy.

However, although more than 400 PRG candidates have been discovered so far, only a dozen of them have been confirmed as true polar ring galaxies by follow-up spectral observations.

Now, a team of astronomers led by Akhil Krishna has discovered another PRG candidate. DES J024008.08-551047.5 (or DJ0240) was detected during visual observations of optical imaging data from DECaLS.

“We detected DJ0240 as a potential PRG candidate with a ring component positioned almost perpendicular to the host galaxy,” the researchers wrote in the paper.

The study found that DJ0240 has a ring positioned almost perpendicular to its host galaxy. The position angle of the ring is about 80 degrees, and the position angle of the host is about 10 degrees, which indicates that the two components are almost perpendicular to each other. The distance to the galaxy is estimated at about 1.8 billion light years.

By analyzing the images, the team found that the ring is three times longer than the host galaxy, which consists of a bulge and a disk. Moreover, the ring has been shown to be bluer than the host, which is usually seen in other known PRGs. The paper’s authors explained that the presence of blue ring components in PRGs indicates a higher level of ongoing star formation activity in these structures.

The researchers found that ring DJ0240 contains a relatively small Sersic index, supporting the PRG classification of this galaxy. They added that the measured effective radii of the galaxy components are comparable to those of other PRGs.

Summing up the results, the astronomers conclude that DJ0240 is most likely a PRG, except that the host galaxy may be a lenticular one. However, more studies are needed in order to draw final conclusions.

“We suggest that ring galaxy DJ0240 is a very promising candidate for inclusion in the PRG catalog. However, further research is necessary to confirm its classification as a PRG, particularly through spectral observations to analyze the kinetic properties of both the host galaxy and the polar galaxy.” Structure, he wrote. Researchers.

more information:
Akhil Krishna R et al., DES J024008.08-551047.5: a new member of the family of polar ring galaxies, arXiv (2023). doi: 10.48550/arxiv.2308.15534

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