An international team of scientists, headed by Dr Darach Watson of the University of Copenhagen in Denmark, has used the X-ray instrument on ESO’s Very Large Telescope along with the Atacama Large Millimeter/submillimeter Array to observe A1689-zD1 – one of the youngest and most distant galaxies ever found.
The extremely distant galaxy A1689-zD1 appears on this picture as the elongated reddish object; its light has been magnified by a factor of more than 9 by the massive gravitational lensing effect of the galaxy cluster Abell 1689. Image credit: J. Richard / ESO.
Dr Watson and his colleagues were surprised to discover a far more evolved system than expected. It had a fraction of dust similar to a very mature galaxy, such as the Milky Way. Such dust is vital to life, because it helps form planets, complex molecules and normal stars.
A1689-zD1 is observable only by virtue of its brightness being amplified more than 9 times by a gravitational lens in the form of the galaxy cluster Abell 1689, which lies between the young galaxy and our Solar System.
Without the gravitational boost, the glow from A1689-zD1 would have been too weak to detect.
“We are seeing A1689-zD1 when the Universe was only about 700 million years old – 5% of its present age,” the astronomers said.
“It is a relatively modest system – much less massive and luminous than many other objects that have been studied before at this stage in the early Universe and hence a more typical example of a galaxy at that time.”
A1689-zD1 is being observed as it was during the epoch of reionization, when the earliest stars brought with them a cosmic dawn, illuminating for the first time an immense and transparent Universe and ending the extended stagnation of the Dark Ages.
Expected to look like a newly formed system, the galaxy surprised the astronomers with its rich chemical complexity and abundance of interstellar dust.
The galaxy seemed to be emitting a lot of radiation in the far infrared, indicating that it had already produced many of its stars and significant quantities of metals, and revealed that it not only contained dust, but had a dust-to-gas ratio that was similar to that of much more mature galaxies.
This spectacular view from the Hubble Space Telescope shows the galaxy cluster Abell 1689. The galaxy A1689-zD1 is located in the box, although it is still so faint that it is barely seen in this picture. Image credit: NASA / ESA / L. Bradley, Johns Hopkins University / R. Bouwens, University of California, Santa Cruz /H. Ford, Johns Hopkins University / G. Illingworth, University of California, Santa Cruz.
“Although the exact origin of galactic dust remains obscure, our findings indicate that its production occurs very rapidly, within only 500 million years of the beginning of star formation in the Universe – a very short cosmological time frame, given that most stars live for billions of years,” said Dr Watson, who is the first author of the paper published in the journal Nature.
“This amazingly dusty galaxy seems to have been in a rush to make its first generations of stars,” added co-author Dr Kirsten Knudsen from the Chalmers University of Technology in Sweden.
The findings suggest A1689-zD1 to have been consistently forming stars at a moderate rate since 560 million years after the Big Bang, or else to have passed through its period of extreme starburst very rapidly before entering a declining state of star formation.
Prior to this result, there had been concerns among astronomers that such distant galaxies would not be detectable in this way, but A1689-zD1 was detected using only brief observations with the Atacama Large Millimeter/submillimeter Array.
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Darach Watson et al. A dusty, normal galaxy in the epoch of reionization. Nature, published online March 2, 2015; doi: 10.1038/nature14164
