by Staff Writers
Copenhagen, Denmark (SPX) Mar 03, 2015
A team of astronomers who set out to observe one of the youngest and most remote galaxies ever found have been surprised to discover a far more evolved system than expected. It had a fraction of dust similar to a very mature galaxy, like the Milky Way.
Their findings have revealed the first detection of dust in such a remote star-forming system, as well as offering tantalizing evidence for the rapid evolution of galaxies after the Big Bang.
The international team of researchers, including from the UK, used the ALMA (Atacama Large Millimeter/submillimeter Array) telescope in Chile, the most powerful radio telescope in the world, to pick up the faint glow from warm dust in the distant galaxy, called A1689-zD1, and used ESO's Very Large Telescope (VLT) to measure its distance.
A1689-zD1 is observable only by virtue of its brightness being amplified more than nine times by a gravitational lens in the form of the spectacular galaxy cluster Abell 1689, which lies between the young galaxy and the Earth. Without the gravitational boost, the glow from this very faint galaxy would have been too weak to detect.
The University of Copenhagen's Professor Darach Watson, who led the research, said: "After confirming the galaxy's distance using the VLT we realized it had previously been observed with ALMA. We didn't expect to find much, but I can tell you we were all quite excited when we realized that not only had ALMA observed it, but that there was a clear detection. One of the main goals of the ALMA observatory was to find galaxies in the early universe from their cold gas and dust emissions -- and here we had it!"
"Although the exact origin of galactic dust remains obscure," explains Professor Watson, "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."
The University of Edinburgh's Dr. Michal Michalowski led the effort of measuring the properties of this distant galaxy to understand its nature. This involved detailed modeling of the galaxy's brightness at a broad range wavelengths, from ultraviolet to far-infrared, and the calculation of the amount of stars and dust it already has, and how fast new supplies are being formed. Moreover, he put A1689-zD1 in the context of other distant galaxies, in order to confirm that it is a typical galaxy in the early universe.
Dr. Michalowski said: "A1689-zD1 has turned out to be a hundred times less massive than the Milky Way, but forming new stars significantly faster. Most of this star formation activity is completely hidden from us by galactic dust, and we have not seen this before at such large distances. ALMA is the only telescope in the world sensitive enough to detect such remote galaxies."
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 ALMA.
Dr. Kirsten Knudsen, from the Onsala Space Observatory in Sweden, and co-author of the paper, added, "This amazingly dusty galaxy seems to have been in a rush to make its first generations of stars. In the future, ALMA will be able to help us to find more galaxies like this, and learn just what makes them so keen to grow up."
The Science and Technology Facilities Council (STFC) subscribes to ESO, giving UK scientists access to ESO's telescopes. It also funded UK participation in this research for the Institute for Astronomy at the University of Edinburgh.
Niels Bohr Institute
Stellar Chemistry, The Universe And All Within It
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