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SA researchers help discover hidden galaxies

Local scientists play a big part in the discovery of 883 galaxies, about half of which had never been seen before.

Admire Moyo
By Admire Moyo, ITWeb's news editor.
Johannesburg, 11 Feb 2016
Professor Renee C Kraan-Korteweg and Dr Anja Schroder helped make the groundbreaking discovery.
Professor Renee C Kraan-Korteweg and Dr Anja Schroder helped make the groundbreaking discovery.

South African researchers have played a big part in making a groundbreaking discovery by peering through the stars and dust of the Milky Way with a radio telescope to discover hidden galaxies beyond.

The local scientists - a leading astronomy researcher from the University of Cape Town and one from the South African Astronomical Observatory (SAAO) - formed part of an international team of scientists that made the discovery.

Professor Ren'ee C Kraan-Korteweg, chair of astronomy at UCT, and her close collaborator, Dr Anja Schr"oder, who is working with the SAAO, are among the lead authors of "The Parkes HI Zone of Avoidance Survey". The paper was published in the Astronomical Journal on Tuesday.

They worked with first author professor Lister Staveley-Smith from the University of Western Australia node of the International Centre for Radio Astronomy Research.

The Great Attractor

Hundreds of hidden nearby galaxies have been discovered for the first time, shedding light, among others, on a mysterious gravitational anomaly dubbed the Great Attractor, the researchers say.

Despite being just 250 million light years from Earth - very close in astronomical terms - the new galaxies had been hidden from view until now by our own galaxy, the Milky Way, they add.

Thanks to the 64m Parkes Radio Telescope, which was equipped with a receiver that can scan the sky 13 times faster than before, the scientists were able to survey this hidden part of the universe much more efficiently. "Even so, the data gathering went on for various years," says Kraan-Korteweg.

The discovery may help to explain the Great Attractor region, which appears to be drawing the Milky Way and hundreds of thousands of other galaxies towards it with a gravitational force suggesting it contains a mass of the order of one million billion suns - our whole Milky Way is moving towards the Great Attractor at two million kilometres per hour.

"The Milky Way is very beautiful, of course, and it's very interesting to study our own galaxy, but it completely blocks out the view of the more distant galaxies behind it," says Staveley-Smith.

Scientists have been trying to get to the bottom of the mysterious Great Attractor since major deviations from universal expansion were first discovered in the 1970s and 1980s. "We don't actually understand what's causing this gravitational acceleration on the Milky Way or where it's coming from," Staveley-Smith adds.

"The team found a total of 883 galaxies, about half of which had never been seen before," says Schr"oder, who scrutinised all available multi-wavelength imaging data for possible counterparts.

Kraan-Korteweg points out the newly identified galaxies provide evidence that the mass over-density called the Great Attractor is due to the existence of a major nearby supercluster - a large collection of galaxies and clusters of galaxies - that crosses the Milky Way diagonally. The research also identified several new structures that could help to explain the movement of the Milky Way, including three galaxy concentrations (named NW1, NW2 and NW3) and two new clusters (named CW1 and CW2).

Asked what the discovery means to the South African astronomy industry, Kraan-Korteweg said: "It does reveal that we in South Africa and our students have been working with innovative radio telescopes instrumentation and data for many years."

Next-gen telescopes

She believes this is relevant for the country's preparedness to lead major science research projects with the new-generation radio telescopes that SA now has, for example KAT7 and those that will be ready soon (MeerKAT) in SA, as well as future strong involvement in the Square Kilometre Array (SKA).

According to Kraan-Korteweg, the process to discover the galaxies was very long. Both Kraan-Korteweg and Schr"oder have been involved in this project since its inception in 1997. This included regular observing runs over many years with the Parkes Radio Telescope in Australia, data reduction, the actual search for signatures of the galaxies in the data, and presenting preliminary results at international conferences.

Both were in charge of preparing major parts of the paper and are working on follow-up analysis, in particular using near-infrared data obtained with the SAAO Infrared Survey Facility using the motions of the detected galaxies to get better estimates of the overall mass density in the nearby universe.

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