Victoria University of Wellington astrophysicists are part of an international team that today releases one of the widest-ever radio wave surveys of the Universe and the first to reveal it in such technicolour detail.
Published in the Monthly Notices of the Royal Astronomical Society, the GaLactic and Extragalactic All-sky MWA, or GLEAM, survey has produced a catalogue of 300,000 galaxies observed at frequencies from 70 to 230 MHz by the Murchison Widefield Array (MWA), a $50 million radio telescope located at a remote site in the West Australian outback.
Victoria Associate Professor of Physics Melanie Johnston-Hollitt and postdoctoral fellows Dr Cathie Zheng and Dr Luke Hindson were the New Zealand arm of a 19-strong multi-country team that designed and executed the survey and processed the data.
Associate Professor Johnston-Hollitt is also Chair of the MWA Executive Board.
GLEAM began collecting data in 2013 and Associate Professor Johnston-Hollitt says the work has significantly expanded the parameters of scientific inquiry and knowledge.
“There are a number of questions we have about the Universe we can use this survey to answer,” she says.
Two studies by Associate Professor Johnston-Hollitt, Dr Zheng, Dr Hindson (now at the University of Hertfordshire in the United Kingdom), former student Luke Pratley (now at University College London) and current Master’s student Stefan Duchesne have already benefited from GLEAM and Associate Professor Johnston-Hollitt is preparing to publish papers on the results.
“We know from other indicators our galaxy should have about 1,000 ‘supernova remnants’—the remains of exploded stars. But before we could only see 300. One of the reasons is because the older, dimmer ones are hard to detect at high frequencies. With GLEAM, observing at lower frequencies, we have been able to find about 20 percent more remnants.
“The other thing my group at Victoria has been working on are ‘galaxy clusters’. Galaxies in the Universe are not distributed uniformly. They cluster together in anything up to thousands of galaxies and those clusters move and at some point collide, producing shockwaves and turbulence on an epic scale. But those shockwaves are very, very faint and when we have looked for signatures of collisions using radio telescopes with higher frequencies we haven’t found that many. Since January, using GLEAM, we have doubled the number previously known—identifying more than 240 radio signatures of shockwaves or turbulence in clusters.”
Lead author of the GLEAM catalogue Dr Natasha Hurley-Walker, from Australia’s Curtin University and International Centre for Radio Astronomy Research (ICRAR), says some of the radio waves observed in the survey have been travelling through space for billions of years.
“The GLEAM survey is a significant accomplishment for the MWA radio telescope and the team of international scientists that worked on it,” says Dr Hurley-Walker.
Completing the survey is a big step on the path to SKA-low, the low frequency part of the international Square Kilometre Array (SKA) radio telescope to be built in Australia in the coming years.
“By mapping the sky in this way, we can help fine-tune the design for the SKA and prepare for even deeper observations into the distant Universe,” says MWA Director Associate Professor Randall Wayth, from Curtin University and ICRAR.
