Gift of galaxies will fuel new findings
Posted: June 4, 2001

Redshift data and spectra from the first 100,000 galaxies measured by the 2dF (Two-degree Field) Galaxy Redshift Survey will be released to the world astronomical community on June 30. Thirty-two researchers from 13 institutions have been carrying out the survey with the Anglo-Australian Telescope near Coonabarabran in eastern Australia. They have now netted more than 175,000 redshifts and will reach the survey target of 250,000 by the end of 2001. Redshift data can be converted to positions in space and so the survey has created the most comprehensive three-dimensional map of the local Universe yet made.

As well as providing by far the largest available set of galaxy spectra for mapping the Universe, the 2dFGRS database is a goldmine of interesting and unusual objects.

"The 2dF dataset is a free gift of 100,000 redshifts to astronomers world-wide. They can apply it immediately to improving our understanding of galaxy evolution and the structure of the Universe," said 2dF survey team co-leader Dr Matthew Colless of the Australian National University.

"For many rare types of objects, we need to have large samples before we can understand the objects' properties and how they are related to their environments," he said.

"For instance, radio telescopes are extremely good at detecting extremely powerful, 'active' galaxies in the very distant universe. But to understand how these galaxies evolve over time, we need also a large sample of such galaxies nearby. This can only be achieved with an optical telescope," Dr Colless said. "Cross-matching the 2dF survey data with large-area radio surveys will give a sample of up to 4,000 radio-emitting galaxies in the local Universe."

A key finding from the data, posted online on May 15, is the first firm evidence that the irregularities in the cosmic microwave background are still imprinted on the distribution of galaxies in today's Universe. The large sample of galaxies generated by the 2dF survey allowed the researchers to measure the characteristics of the galaxy distribution with very small random errors. "These subtle over-densities in the galaxy distribution range in size from about 300 million to 1.5 billion light-years," said team co-leader Prof. John Peacock of the University of Edinburgh.

The same study also found that 'normal' (baryonic) matter makes up only 15% of the Universe's total matter - the rest being the unidentified 'dark matter'. And total matter is only 35% of the Universe's contents, according to another 2dF finding in 'Nature' on March 8. (The rest is believed to be 'dark energy'.)

The 2dF dataset will also be used to test theories of cosmological inflation, the extremely rapid growth of the Universe just after the Big Bang.

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 survey covers a total area of about 2,000 square degrees, selected from both northern and southern skies.

The 2dF Galaxy Redshift Survey has been made possible by the dedicated efforts of the staff of the Anglo-Australian Observatory, both in creating the 2dF instrument and in supporting it on the telescope.