Astronomers spun up by galaxy-shape finding

For the first time astronomers have measured how a galaxy’s spin affects its shape.

It sounds simple, but measuring a galaxy’s true 3D shape is a tricky problem that astronomers first tried to solve 90 years ago.

“This is the first time we’ve been able to reliably measure how a galaxy’s shape depends on any of its other properties – in this case, its rotation speed,” said research team leader Dr Caroline Foster of the University of Sydney.

The study was published on 11 September in the journal Monthly Notices of the Royal Astronomical Society.

Galaxies can be shaped like a pancake, a sea urchin or a football, or anything in between.

Faster-spinning galaxies are flatter than their slower-spinning siblings, the team found.

“And among spiral galaxies, which have disks of stars, the faster-spinning ones have more circular disks,” said team member and CAASTRO Chief Investigator, Professor Scott Croom of The University of Sydney.

The team made its findings with SAMI (the Sydney-AAO Multi-object Integral field unit), an instrument jointly developed by The University of Sydney and the Australian Astronomical Observatory with funding from CAASTRO.

SAMI gives detailed information about the movement of gas and stars inside galaxies. It can examine 13 galaxies at a time and so collect data on huge numbers of them.

Dr Foster’s team used a sample of 845 galaxies, over three times more than the biggest previous study. This large number was the key to solving the shape problem.

Because a galaxy’s shape is the result of past events such as merging with other galaxies, knowing its shape also tells us about the galaxy’s history.

Publication

C. Foster and 19 coauthors, “The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies”. Monthly Notices of the Royal Astronomical Society(2017) https://doi.org/10.1093/mnras/stx1869The ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) is a collaboration between The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the last two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.

Contacts

Dr Caroline Foster (University of Sydney)
Ph: +61 2 8627 6411        E: Caroline.Foster@sydney.edu.au

Professor Scott Croom (University of Sydney, CAASTRO)
Ph: +61 2 9036 5311        E: Scott.Croom@sydney.edu.au

Helen Sim (CAASTRO)
Ph: +61 419 635 905        E: Helen.Sim@sydney.edu.a