Why massive galaxies don’t dance in crowds

Why massive galaxies don’t dance in crowds

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
lighter neighbours.

“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
, 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

Explore further:

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).
DOI: 10.3847/1538-4357/aa7a11

Journal reference: Astrophysical

Provided by: University
of New South Wales