In a newly published study, a team of astronomers measures 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. However, for the first time astronomers have measured how a galaxy’s spin affects its shape, in new research published in the journal Monthly Notices of the Royal Astronomical Society.
“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.
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 discs of stars, the faster-spinning ones have more circular discs,” said team member Prof 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, the ARC Centre of Excellence for All-sky Astrophysics.
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: “The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies,” C. Foster, J. Van de Sande, F. D’Eugenio, et al., Monthly Notices of the Royal Astronomical Society (2017) 472 (1) (DOI: 10.1093/mnras/stx1869).