Galaxy cluster Abell 2744, imaged with the Hubble Space
Telescope. The cluster lies in the constellation of Sculptor
and contains several hundred galaxies. Credit: NASA, ESA, and
R. Dupke (Eureka Scientific, Inc.), et al.
Scientists have discovered why heavyweight galaxies living in
a dense crowd of galaxies tend to spin more slowly than their
“Contrary to earlier thinking, the spin rate of the galaxy is
determined by its mass, rather than how crowded its
neighbourhood is,” says study first author Associate Professor
Sarah Brough of UNSW Sydney and the ARC Centre of Excellence
for All-sky Astrophysics, CAASTRO.
The finding, based on a detailed study of more than 300
galaxies, is published in the Astrophysical
To measure how fast their galaxies rotated, the researchers
used an instrument called the Sydney-AAO Multi-object Integral
field spectrograph (SAMI) on the 4-metre Anglo-Australian
Telescope in eastern Australia.
SAMI ‘dissects’ galaxies, obtaining optical spectra from 61
points across the face of each galaxy, 13 galaxies at a time.
“We want to know which factors really drive how galaxies
evolve,” says team member Dr Matt Owers of the Australian
Astronomical Observatory and Macquarie University. “In this
case, we’ve sorted out nature versus nurture.”
The new finding runs counter to previous studies, made with
smaller samples of galaxies, which concluded that a galaxy’s
spin rate is determined by the other galaxies in its
Associate Professor Brough says this earlier conclusion was
spurious. “Once you take into account the strong association
with mass, there’s no link between a galaxy’s spin rate and its
environment,” she says.
Credit: University of New South Wales
Scientists unveil new 3-D view of galaxies
More information: Sarah Brough et al. The SAMI Galaxy
Survey: Mass as the Driver of the Kinematic Morphology–Density
Relation in Clusters, The Astrophysical Journal (2017).