Galaxy patterns reveal missing link to Big Bang

Australian astronomers from the Anglo-Australian Observatory, The Australian National University and the University of New South Wales, together with their UK colleagues, today announced that they have found the 'missing link' that directly relates modern galaxies like our own Milky Way to the Hot Big Bang that created our Universe 14 thousand million years ago.

This is the result of a 10-year effort to map the 3D distribution in space of 220,000 galaxies using the 3.9-m Anglo-Australian Telescope (AAT) in New South Wales – a project called the 2-degree Field Galaxy Redshift Survey (2dFGRS).

This survey was almost ten times larger than any previous such study.

It measured in detail patterns in the distribution of galaxies, on scales from 100 million to 1 billion light-years.

Subtle features in these patterns were set by physical processes that operated when the universe was very young, and reveal the 'missing link' between present-day galaxies and the Big Bang.

“This is an enormously important finding,” said Dr Matthew Colless, Director of the Anglo-Australian Observatory and Australian leader of the 2dFGRS team. “Although there have been hints before of these features, this is the first high-confidence detection. We’ve confirmed that gravity was the driving force that created today’s galaxies.”

“The same features tell us the mass density of the Universe – the amount of mass for a given volume of space – with an uncertainty of less than 10 per cent.”

“This survey, coupled with a few other lines of enquiry, has given us extremely good measurements of two major constituents of the Universe – its dark matter and dark energy,” said 2dFGRS team member Dr Warrick Couch of the University of New South Wales.

Measuring the galaxies distances and modelling their distribution in space had taken “more than a decade of work” by a team of over 30 people, said Dr Bruce Peterson of the Research School of Astronomy and Astrophysics at ANU, the 2dFGRS team member who constructed the database for the survey.

Independent corroboration of the 2dFGRS result was also announced today by the US-led Sloan Digital Sky Survey (SDSS), at the winter meeting of the American Astronomical Society in San Diego. The SDSS team used a sample of 46,000 highly luminous red galaxies and a different method of analysis from the 2dFGRS team’s. “Happily, the two groups’ conclusions are consistent,” said 2dFGRS team member Dr Joss Hawthorn of the Anglo-Australian Observatory.

The robotic 2dF instrument, which made the survey possible, was designed and built by the Anglo-Australian Observatory. It measures the ‘redshifts’ of galaxies – a change in the light they emit that varies with distance, and which can be used as a measure of distance. “The 2dF instrument is the world’s most efficient machine for measuring redshifts,” said 2dFGRS team member Dr Russell Cannon, a former director of the Anglo-Australian Observatory during whose term the 2dFGRS had been initiated.

Matching ripples

Theorists in the 1960s suggested that the primordial seeds of galaxies should be seen as ‘ripples’ – a pattern of hotter and cooler spots – in the cosmic microwave background (CMB). This CMB is heat radiation left over from the Big Bang. We see the CMB as it was when the Universe was only 350,000 years old.

The ripples in the CMB were first seen in 1992 by NASA’s COBE satellite. But until now, no-one had been able to definitely show how they were connected to galaxy formation.

Astronomers use a statistic called the ‘power spectrum’ to mathematically describe the pattern of spots in the CMB. A plot of the power spectrum has peaks and troughs in it, and describes how the spots are clustered on different scales. The 2dFGRS team has produced the same kind of power spectrum for the galaxies that they mapped out.

“Features in the 2dFGRS power spectrum match up with features in the power spectrum of the CMB,” said 2dFGRS team member Dr Simon Driver of the ANU Research School of Astronomy and Astrophysics. “This leaves no doubt that we’ve finally identified the origin of galaxies.”

Weighing the Universe

The same features in the power spectrum have allowed the 2dFGRS team to 'weigh' the universe with unprecedented accuracy.

These features – called the "baryon wiggles" – contains information about the contents of the universe; in particular about the amount of ordinary matter – particles called baryons – that makes up stars, planets and people.

The 2dFGRS has shown that baryons are a small component of our universe, making up a mere 18% of the total mass. The remaining 82% is dark matter. For the first time, the 2dFGRS team have measured the density of matter in the Universe with an uncertainty of less than 10 per cent.

Furthermore, the 2dFGRS has also shown that all the mass in the universe (both luminous and dark) is outweighed 4:1 by an even more exotic component called "vacuum energy" or "dark energy".  This has antigravity properties, causing the expansion of the universe to speed up. This conclusion comes from combining 2dFGRS results with data on the cosmic microwave background radiation. The origin and identity of the dark energy remains one of the deepest mysteries of modern science.

Astronomers believe they could find clues to the identity of dark energy by identifying baryon wiggles in the pattern of galaxies that existed when the Universe was half its present age. They are now planning huge galaxy surveys to do this. “The Anglo-Australian Observatory has a radical new design concept for an instrument to make such a mega-survey,” said Dr Hawthorn.

NOTES

The 2dF Instrument
Designed and built by the Anglo-Australian Observatory, the 2dF is one of the world's most complex astronomical instruments, able to capture 400 spectra simultaneously. A robot arm positions up to 400 optical fibres on a field plate, each to within an accuracy of 20 micrometres. Light from up to 400 objects is collected and fed into two spectrographs for analysis. The expansion of the Universe shifts galaxy spectra to longer wavelengths.
By measuring this "redshift" in a galaxy's spectrum, the galaxy's distance can be determined.

The 2dF Galaxy Redshift Survey used the 2dF to cover a total area of about 2,000 square degrees, selected from both northern and southern skies. It used about 250 nights observing time on the 3.9m-diameter Anglo-Australian Telescope during 1995-2002.

The 2dF Galaxy Redshift Survey is nearly ten times larger than the surveys that preceded it.
 
2dF Galaxy Redshift Survey Team
Members of the team are based at the following institutions:
Anglo-Australian Observatory, The Australian National University, California Institute of Technology, CSIRO Australia Telescope National Facility, ETH Zurich, Johns Hopkins University, Liverpool John Moores University, University of Cambridge, University of Durham, University of Edinburgh, University of Leeds, University of New South Wales, University of Nottingham, University of Oxford, University of St Andrews.

Publication
A paper on the finding, The 2dF Galaxy Redshift Survey: Power Spectrum Analysis and the final dataset and cosmological implications, is posted on the astrophysics preprint server (Australian mirror site, http://au.arxiv.org/archive/astro-ph) and is also available at http://www.mso.anu.edu.au/2dFGRS/Public/Publications/power-spectrum_cosmology.pdf/.
It has been submitted to Monthly Notices of the Royal Astronomical Society for publication.

A meeting to review the successes of 2dF will be held at the RAS on January 13 and 14th. See http://www.ras.org.uk/html/meetings/RAS2004.html#jan for details.

ANU CONTACTS 

Dr Bruce Peterson, Research School of Astronomy and Astrophysics, The Australian National University
T: 02-6125-8035 / 02-6231-2971 (home)
M: 0413-967-397
peterson@mso.anu.edu.au

Dr Simon Driver, Research School of Astronomy and Astrophysics, The Australian National University
T: 02-6125-0222 / 02-6231-3120 (home)
spd@mso.anu.edu.au

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