Why Massive Galaxies Don’t Dance In Crowds

Contrary to previous research, the spin rate of galaxies is actually determined by mass instead of their interactions with neighboring galaxies.

AsianScientist (Aug. 21, 2017) – Scientists have discovered that mass, rather than interactions with the nearby environment, determines the spin rate of galaxies. The finding, based on a detailed study of more than 300 galaxies, is published in The Astrophysical Journal.

“Contrary to earlier thinking, the spin rate of the galaxy is determined by its mass, rather than how crowded its neighborhood is,” said Associate Professor Sarah Brough of the University of New South Wales, Sydney, and the ARC Centre of Excellence for All-sky Astrophysics.

To measure how fast their galaxies rotated, the researchers used an instrument called the Sydney-Australian Astronomical Observatory Multi-object Integral field spectrograph (SAMI) on the four-meter 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,” said 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 neighborhood.

“Once you take into account the strong association with mass, there’s no link between a galaxy’s spin rate and its environment,” she added.

The article can be found at: Brough et al. (2017) The SAMI Galaxy Survey: Mass as the Driver of the Kinematic Morphology–Density Relation in Clusters.


Source: University of New South Wales; Photo: NASA.
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