April 1, 2008
Astronomers Find Evidence of Earliest Star Formation
New measurements from some of the most distant galaxies bolster the evidence that the strongest burst of star formation in the history of the Universe occurred about two billion years after the Big Bang. An international team of astronomers from the UK, France, Germany and the USA have found evidence for a dramatic surge in star birth in a newly discovered population of massive galaxies in the early Universe.
In his talk at the RAS National Astronomy Meeting in Belfast on Tuesday 1 April, team member Dr Scott Chapman from the Institute of Astronomy in Cambridge will present observations of five of these galaxies that are forming stars at a tremendous rate and have large reservoirs of gas that will power the star formation for hundreds of millions of years. Dr Chapman's work is supported by a parallel study made by PhD student Caitlin Casey, who finds that the star formation in the new galaxies is distributed over a vast area.
The galaxies are so distant that the light we detect from them has been traveling for more than 10 billion years. This means that we see them as they were about a three billion years after the Big Bang. The recent discovery of a new type of extremely luminous galaxy in this epoch - one that is very faint in visible light, but much brighter at longer, radio wavelengths - is the key to the new results.
A related type of galaxy was first found in 1997 (but not well understood until 2003) using a new and much more sensitive camera that detects radiation emitted at submillimeter wavelengths (longer than the wavelengths of visible light that we see with but somewhat shorter than radio waves). The camera, called `SCUBA' was attached to the James Clerk Maxwell Telescope (JCMT), on Mauna Kea in Hawaii.
In 2004 the Cambridge-led team of astronomers proposed that these distant "submillimeter-galaxies" might only represent half of the picture of rapid star formation in the early Universe, as SCUBA is biased towards colder objects. They suggested that a population of similar galaxies with slightly hotter temperatures could exist but have gone largely unnoticed.
The team of scientists searched for the missing galaxies using observatories around the world: the MERLIN array in the UK, the Very Large Array (VLA) in the US (both radio observatories), the Keck optical telescope on Hawaii and the Plateau de Bure submillimeter observatory in France. The instruments found and pinpointed the galaxies, measured their distances and then confirmed their star forming nature through the detection of the vastly extended gas and dust.
The new galaxies have prodigious rates of star formation, far higher than anything seen in the present-day Universe. They probably developed after the first stars and galaxies had already formed in what would have been a perfectly smooth Universe. None the less, studying these new objects gives astronomers an insight into the earliest epochs of star formation after the Big Bang.
With the new discovery, the Cambridge astronomers have provided a much more accurate census of some of the most extreme galaxies in the Universe at the peak of their activity. Future observations will investigate the details of the galaxies' power source and try to establish how they will develop once their intense bursts of activity come to an end.
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Plateau de Bure Interferometer