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Galaxy survey maps where matter lurks

1er avril 2009

Astronomers from Australia, the UK, USA, South Africa, France and Japan have just completed the most detailed survey of galaxies in the nearby Universe, which will reveal not only where the galaxies are but also where they’re heading, how fast, and why. "It’s like taking a snapshot of wildebeest on the African plain. We can tell which waterholes they’re heading to, and how fast they’re travelling," said D. Heath Jones of the Anglo-Australian Observatory (AAO), lead scientist for the Six-Degree Field Galaxy Survey (6dFGS).

Galaxies are tugged around by each other’s gravity. By measuring the galaxies’ movements, the researchers can map the gravitational forces at work in the local Universe, and so show how matter, seen and unseen, is distributed.

Giant superclusters of galaxies are huge concentrations of mass, but they can’t be weighed accurately by looking at their light alone.

Results from the survey were presented on 1 April at an international meeting in Malaysia by Matthew Colless, Director of the Anglo-Australian Observatory (AAO). The survey was carried out with the 1.2-m UK Schmidt Telescope, which is operated by Siding Spring Observatory in New South Wales, Australia. Broader and shallower than previous comparable surveys — it covered twice as much sky as the Sloan Digital Sky Survey — it has recorded the positions of more than 110 000 galaxies over more than 80% of the Southern sky, out to about two thousand million light-years from Earth [a redshift of 0.15].

Figure 1 : La distribution dans l’espace d’environ 100 000 galaxies obtenues par l’arpentage 6dF. Chacune d’elle est représentée par un point, Notre Galaxie se trouve au centre de l’image. Source : Chris Fluke, Centre for Astrophysics and Supercomputing, Swinburne University of Technology. Cliquer sur l’image pour l’agrandir

he survey shows strings and clusters of nearby galaxies on large scales in unprecedented detail, and has revealed more than 500 voids — "empty" areas of space with no galaxies. The special aspect of this survey is that it will let the researchers disentangle two causes of galaxy movements. As well as being pulled on by gravity, galaxies also ride along with the overall expansion of the Universe. For about 10% of their galaxies, the 6dFGS researchers will tease apart these two velocity components : the one associated with the Universe’s expansion, and the one representing a galaxy’s individual, "peculiar", motion. The peculiar velocities collected as part of this survey number more than five times as many as in any previous survey.

Figure 2 : La coupole du télescope de Schmidt avec lequel l’arpentage a été réalisé.

Reference

  • The 6dF Galaxy Survey : Final Data Release (DR3) and Southern Large Scale Structures Jones D Heath., Read Mike A., Saunders Will., Colless Matthew., Jarrett Tom., Parker Quentin., Fairall Anthony., Mauch Thomas., Sadler Elaine., Watson Fred., Burton Donna., Campbell Lachlan., Cass Paul., Croom Scott., Dawe John., Fiegert Kristin., Frankcombe Leela., Hartley Malcolm., Huchra John., James Dionne., Kirby Emma., Lahav Ofer., Lucey John., Mamon Gary., Moore Lesa., Peterson Bruce., Prior Sayuri., Proust Dominique., Russell Ken., Safouris Vicky., Wakamatsu Ken-ichi., Westra Eduard., Williams Mary : 2009, submitted to Monthly Notices of the Royal Astronomical Society

Contact

  • Dominique Proust (Observatoire de Paris, GEPI, et CNRS)
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