A group of international astronomers, including scientists from Queen’s University, has determined two possible polar ring galaxies.
The study has been recently reported in the Monthly Notices of the Royal Astronomical Society.
Queen’s scientists Nathan Deg and Kristine Spekkens (Physics, Engineering Physics, and Astronomy) headed the analysis of data obtained with the help of a telescope that has been owned and operated by CSIRO, Australia’s national science agency.
By examining sky maps of hydrogen gas in more than 600 galaxies within the framework of CSIRO's ASKAP radio telescope's WALLABY survey, researchers have detected two potential polar ring galaxies. These galaxies belong to a distinctive category characterized by a ring of stars and gas that runs perpendicular to their primary spiral disk.
Even though this is not the first time that astronomers have noted polar ring galaxies, they are the first observed with the help of the ASKAP telescope situated at Inyarrimanha Ilgari Bundara, CSIRO’s Murchison radio astronomy observatory on Wajarri Yamaji Country in Western Australia.
Such new detections in gas alone indicate that polar ring galaxies may be more common than earlier believed.
Understanding How Galaxies Evolve
Additional examination of polar ring structures could help us better comprehend how galaxies develop. For instance, one of the primary hypotheses to describe the origin of polar rings is a merger where a larger galaxy “swallows” a smaller one.
If polar ring galaxies are more prevalent, this could mean that these mergers are more frequent.
In the future, polar ring galaxies could also be utilized to intensify the knowledge of the universe, with possible applications in dark matter research. It is feasible to utilize polar rings to examine the shape of dark matter of the host galaxy, which could result in new clues regarding the puzzling properties of the subtle substance.
Visualizing Polar Ring Galaxies
Jayanne English, a member of the WALLABY research group and also an expert in astronomy image-making at the University of Manitoba, came up with the first images of such gaseous polar ring galaxies utilizing a combination of optical and radio data from various telescopes.
Initially, optical and infrared data from the Subaru telescope in Hawaii offered the image of the galaxy’s spiral disk. Further, the gaseous ring was added depending on data that has been achieved from the WALLABY survey, an international project utilizing CSIRO’s ASKAP radio telescope to detect atomic hydrogen emission from nearly half a million galaxies.
The making of this and other astronomical images are all composite since they include information that is not possible to be captured by the eyes. In this specific case, the cold hydrogen gas component, which is invisible to the human eye, is observed in radio “light” with the help of CSIRO’s ASKAP.
The presence of a subtle color gradient of this ring constitutes the orbital motions of the gas, with purple-ish tints at the bottom tracing gas that tends to move toward the viewer while the top portion backs away.
The emission from the ring was isolated from the radio emission originating from the disk of the galaxy with the help of virtual reality tools in partnership with Professor Tom Jarrett (University of Cape Town, South Africa).
More than 25 global collaborators from Canada, South Africa, Australia, Ecuador, Burkina Faso, China, Germany, and beyond worked collectively to examine the data from the first public data release of the WALLABY survey, leading to the newly published paper.
The next step for the team is to verify the polar ring galaxies finding via extra observations using various telescopes, such as the MeerKAT radio telescope in South Africa.
Polar ring galaxies are some of the most spectacular looking galaxies in the Universe. These findings suggest that one to three per cent of nearby galaxies may have gaseous polar rings, which is much higher than suggested by optical telescopes.
Dr. Nathan Deg, Study Lead Author and Researcher, Department of Physics, Engineering Physics and and Astronomy, Queen’s University
Deg added, “These results are a really nice illustration of the tremendous value of mapping the sky more deeply and more widely than has ever been done before. This is serendipity at its best: we found things we certainly didn’t expect to find.”
Dr. Kristine Spekkens, Professor (cross-appointed from Royal Military College), Department of Physics, Engineering Physics & and Astronomy, Queen’s University, Canada adds, “I’m excited to work with such a diverse and collaborative team. We were able to work with data that showed a fine grid of velocity channels, which are equivalent to the radio stations on your old-fashioned radio receiver.”
The richness of the velocity data meant I could assign multiple colours to this composite to subtly convey the motion happening within the polar ring. The dance and choreography of the gas are beautiful, and that motion of the gas gives us some clues as to how galaxies evolve over time.
Dr. Jayanne English, Department of Physics and Astronomy, University of Manitoba
“Our ASKAP radio telescope is delivering a flood of data and we are ready for it. Using ASKAP, full WALLABY will deliver more than 200,000 hydrogen-rich galaxies among them many unusual objects like polar rings, which can be used to probe the shape and distribution of the dark matter halos,” says Dr Bärbel Koribalski, Senior Principal Research Scientist, CSIRO
“These new ASKAP observations, which reveal astonishing ring-like structures around otherwise normal-looking spiral galaxies, suggest that the accretion of gas through interactions with gas-rich companion galaxies is much more common than we previously believed. WALLABY will be an amazing resource to uncover many more of such systems in the future,” notes Professor Lister Staveley-Smith, WALLABY Co-Principal Investigator and Interim Executive Director. ICRAR
One of the most exciting outcomes of a large survey such as WALLABY, which will scan most of the Southern sky to carry out the largest census of neutral atomic hydrogen ever done, is discovering the unexpected -- these unusual galaxies with beautiful gas rings are perfect examples of this.
Barbara Catinella, Study Co-Author and Assistant Professor and WALLABY Co-Principal Investigator, The University of Western Australia
Deg, N., et al. (2023) WALLABY pilot survey: the potential polar ring galaxies NGC 4632 and NGC 6156 Get access Arrow. Monthly Notices of the Royal Astronomical Society. doi.org/10.1093/mnras/stad2312.