A new study, led by University of Sydney astronomer Caroline Foster, is the first to confirm that increased rotation alters the shape of galaxies: faster-spinning galaxies are flatter than their slower-spinning siblings.
A selection of SAMI galaxies imaged with NAOJ’s Subaru Telescope. Image credit: National Astronomical Observatory of Japan / Caroline Foster, University of Sydney / Dan Taranu, University of Western Australia.
“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,” Dr. Foster said.
Galaxies can be shaped like a pancake, a sea urchin or a football, or anything in between.
The faster a galaxy spins, the flatter it becomes, Dr. Foster and co-authors found.
“And among spiral galaxies, which have disks of stars, the faster-spinning ones have more circular disks,” said University of Sydney Professor Scott Croom, co-author of the study.
The astronomers made their findings with the unique SAMI (Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph) instrument on the 3.9-m Anglo-Australian Telescope at Siding Spring Observatory near Coonabarabran, New South Wales, Australia.
“SAMI can examine 13 galaxies at a time and so collect data on huge numbers of them,” the researchers said.
“The new technology in SAMI called ‘hexabundles’ allows us to see galaxies in 3D,” added University of Sydney and Australian Astronomical Observatory senior research fellow Dr. Julia Bryant.
“Through these 3D ‘glasses’ we can not only see what each of the thousands of galaxies looks like, but also see in detail how their gas and stars move.”
The team used a sample of 845 galaxies, over three times more than the biggest previous study.
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.
The findings will be published in the November 21, 2017 issue of the Monthly Notices of the Royal Astronomical Society and are available online.
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C. Foster et al. 2017. The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies. MNRAS 472 (1): 966-978; doi: 10.1093/mnras/stx1869
