A Hubble Space Telescope image of a galaxy cluster (Abell S0740) within the area of sky covered by the 6dF Galaxy Survey.
Galaxy survey shows where matter lurks
3 Apr 2009
Astronomers from Australia, the UK and the USA 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 Dr 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.
"Light can be obscured, but you can't hide gravity," said Dr Jones.
Results from the survey were presented on April 1 at an international meeting in Malaysia by Professor Matthew Colless, Director of the Anglo-Australian Observatory (AAO).
< The UK Schmidt Telescope at Siding Spring Observatory.
The survey was carried out with the 1.2m 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 per cent of the Southern sky, out to about two thousand million light-years from Earth [a redshift of 0.15].
The 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.
The clustering pattern of about 100,000 nearby galaxies, revealed by the 6dF Galaxy Survey. Each galaxy is shown as a dot. The galaxy we live in is at the centre of the pattern.
As well as being pulled on by gravity, galaxies also ride along with the overall expansion of the Universe.
For about 10 per cent 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," said Professor Elaine Sadler of the University of Sydney, a 6dFGS team member.
Adapted from information issued by AAO / Dr Chris Fluke, Centre for Astrophysics and Supercomputing, Swinburne University of Technology / NASA, ESA and The Hubble Heritage Team (STScI/AURA) / Shaun Amy.
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