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Astronomers discover galaxy wrapped in a ribbon
from Contact 14
BY JAMES CHESTERS (CSIRO)
A study by an international team of astronomers using CSIRO’s ASKAP radio telescope suggests that unusual polar ring galaxies may be more common than we think.
The small spiral galaxy NGC 4632 lies surrounded by a ring of cool hydrogen gas, stretching like a delicate ribbon made of cosmic dust, gas and stars at right angles to its spiral disk. It can only be detected by highly sensitive radio telescopes like ASKAP, which is located on Wajarri Country in Western Australia.
It’s one of two potential polar ring galaxies described in a new paper in the Monthly Notices of the Royal Astronomical Society.
Prof. Kristine Spekkens, SKA Canadian Science Director, led the research with Dr Nathan Deg for Queen’s University in Canada, as part of ASKAP’s WALLABY survey.
“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,” Prof. Spekkens said. “This is serendipity at its best: we found things we certainly didn’t expect to find.”
Assuming that NGC 4632 and the more distant galaxy NGC 6156 are polar ring galaxies, researchers calculated the proportion that can be detected in the WALLABY survey. Based on this calculation and the size distribution of the galaxies, the results suggest 1% to 3% of nearby galaxies might have polar rings. This is much higher than suggested by observations from optical telescopes.
Although not the first polar ring galaxies found, these would be the first observed using ASKAP.
CSIRO’s Dr Bärbel Koribalski, co-author of the paper and one of the founders of WALLABY, said the survey will observe the whole southern sky to detect and visualise the gas distribution in hundreds of thousands of galaxies. So far it has mapped 600 galaxies in its pilot phase.
“Using ASKAP over the coming years, we expect to reveal more than 200,000 hydrogen-rich galaxies, among them many more unusual galaxies like these,” Dr Koribalski said.
Why polar rings exist is still a puzzle. One explanation is that their stellar rings, which appear blended with gas clouds, may be shredded material cannibalised from a passing galaxy.
In the future, the enigmatic galaxies can be used to learn more about dark matter, using the polar rings to probe the shape of dark matter, which could give new clues about its mysterious properties.
ASKAP is part of CSIRO’s Australia Telescope National Facility and is a precursor to the SKA telescopes currently being built in Australia and South Africa. CSIRO’s ASKAP telescope is located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio Astronomy Observatory. We acknowledge the Wajarri Yamaji as the Traditional Owners and native title holders of the observatory site.
