Astronomers spun up by galaxy-shape finding

Galaxies from the SAMI survey, imaged with Japan’s Subaru
telescope. Credit: D. Taranu (University of Western Australia),
C. Foster (University of Sydney), NAOJ (the National
Astronomical Observatory of Japan)

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, who completed this
research while working at the Australian Astronomical
Observatory.

The study is published today 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 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 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, the ARC
Centre of Excellence for All-sky Astrophysics.

The SAMI instrument at the 3.9m Anglo-Australian Telescope.
Each silver cable holds a ‘hexabundle’ of special optical fibres
that can look at several different points across the face of a
single galaxy. SAMI can study 13 galaxies at a time. The orange
cables also hold optical fibres: these are used for calibration
purposes. Credit: Ángel R. López-Sánchez.

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.

Explore further:

Scientists unveil new 3-D view of galaxies

More information: Monthly Notices of the Royal
Astronomical Society
(2017). doi.org/10.1093/mnras/stx1869

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by: University
of Sydney