The famous fictional detective Sherlock Holmes used a magnifying lens to reveal barely visible but important evidence. Astronomers are now combining the power of many telescopes on Earth and in space  with a vastly larger form of lens to study a case of vigorous star formation in the early Universe.
"While astronomers are often limited by the power of their telescopes, in some cases our ability to see detail is hugely boosted by natural lenses, created by the Universe," explains lead author Hugo Messias of the Universidad de Concepción (Chile) and the Centro de Astronomia e Astrofísica da Universidade de Lisboa (Portugal), "Einstein predicted in his theory of general relativity that, given enough mass, light does not travel in a straight line but will be bent in a similar way to light refracted by a normal lens."
These cosmic lenses are created by massive structures like galaxies and galaxy clusters, which deflect the light from objects behind them due to their strong gravity — an effect, called gravitational lensing. The magnifying properties of this effect allow astronomers to study objects that would not be visible otherwise and to directly compare local galaxies with much more remote ones, seen when the Universe was significantly younger.
But for these gravitational lenses to work, the lensing galaxy, and the one far behind it, need to be very precisely aligned.
"These chance alignments are quite rare and tend to be hard to identify," adds Messias, "but, recent studies have shown that by observing at far-infrared and millimetre wavelengths we can find these cases much more efficiently."
H-ATLAS J142935.3-002836 (or just H1429-0028 for short) is one of these sources and was found in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). It is among the brightest gravitationally lensed objects in the far-infrared regime found so far, even though we are seeing it at a time when the Universe was just half its current age.
Probing this object was at the limit of what is possible, so the international team of astronomers started an extensive follow-up campaign using the NASA/ESA Hubble Space Telescope alongside other space telescopes and some of the most powerful telescopes on the ground — including the Atacama Large Millimeter/submillimeter Array (ALMA), the Keck Observatory, the Karl Jansky Very Large Array (JVLA), and others. The different telescopes provided different views, which could be combined to get the best insight yet into the nature of this unusual object.
The Hubble and Keck images revealed a detailed gravitationally-induced ring of light around the foreground galaxy. These high resolution images also showed that the lensing galaxy is an edge-on disc galaxy — similar to our galaxy, the Milky Way — which obscures parts of the background light due to the large dust clouds it contains.
"We need to observe with Hubble to find cases of gravitational lensing and to highlight in high resolution the clues left by these huge cosmic lenses", adds Rob Ivison, co-author and ESO's Director for Science
But, it is not possible to see past the large dust clouds of the foreground galaxy with Hubble. The obscuration was overcome by ALMA and the JVLA, since these two facilities observe the sky at longer wavelengths, which are unaffected by dust. Using the combined data the team discovered that the background system was actually an ongoing collision between two galaxies.
Further characterisation of the object was undertaken by ALMA which traced carbon monoxide, allowing for detailed studies of star formation mechanisms in galaxies and for the motion of the material in the galaxy to be measured. This confirmed that the lensed object is indeed an ongoing galactic collision forming hundreds of new stars each year, and that one of the colliding galaxies still shows signs of rotation; an indication that it was a disc galaxy just before this encounter.
The system of these two colliding galaxies resembles the Antennae Galaxies an object much closer to us than H1429-0028 and which Hubble has imaged several times before in stunning detail. This is a spectacular collision between two galaxies, which are believed to have had a disc structure in the past. While the Antennae system is forming stars with a total rate of only a few tens of times the mass of our Sun each year, H1429-0028 each year turns more than 400 times the mass of the Sun of gas into new stars each year.
Ivison concludes: "With the combined power of Hubble and these other telescopes we have been able to locate this very fortunate alignment, take advantage of the foreground galaxy's lensing effects and characterise the properties of this distant merger and the extreme starburst within it. It is very much a testament to the power of telescope teamwork."
 The telescopes and surveys that were employed were: the NASA/ESA Hubble Space Telescope, ALMA, APEX, VISTA, the Gemini South telescope, the Keck-II telescope, the NASA Spitzer Space Telescope, the Jansky Very Large Array, CARMA, IRAM, and SDSS and WISE.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
This research was presented in a paper entitled "Herschel-ATLAS and ALMA HATLAS J142935.3-002836, a lensed major merger at redshift 1.027", by Hugo Messias et al., to appear online on 26 August 2014 in the journal Astronomy & Astrophysics.
The team is composed of Hugo Messias (Universidad de Concepción, Barrio Universitario, Chile, and Centro de Astronomia e Astrofísica da Universidade de Lisboa, Portugal), Simon Dye (School of Physics and Astronomy, University of Nottingham, UK), Neil Nagar (Universidad de Concepción, Barrio Universitario, Chile), Gustavo Orellana (Universidad de Concepción, Barrio Universitario, Chile), R. Shane Bussmann (Harvard-Smithsonian Center for Astrophysics, USA), Jae Calanog (Department of Physics & Astronomy, University of California, USA), Helmut Dannerbauer (Universität Wien, Institut für Astrophysik, Austria), Hai Fu (Astronomy Department, California Institute of Technology, USA), Edo Ibar (Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Chile), Andrew Inohara (Department of Physics & Astronomy, University of California, USA), R. J. Ivison (Institute for Astronomy, University of Edinburgh, Royal Observatory, UK; ESO, Garching, Germany), Mattia Negrello (INAF, Osservatorio Astronomico di Padova, Italy), Dominik A. Riechers (Astronomy Department, California Institute of Technology, USA; Department of Astronomy, Cornell University, USA),Yun-Kyeong Sheen (Universidad de Concepción, Barrio Universitario, Chile), Simon Amber (The Open University, UK), Mark Birkinshaw (H H Wills Physics Laboratory, University of Bristol, UK; Harvard-Smithsonian Center for Astrophysics, USA), Nathan Bourne (School of Physics and Astronomy, University of Nottingham, UK), Dave L. Clements (Astrophysics Group, Imperial College London, UK), Asantha Cooray (Department of Physics & Astronomy, University of California, USA; Astronomy Department, California Institute of Technology, USA), Gianfranco De Zotti (INAF, Osservatorio Astronomico di Padova, Italy), Ricardo Demarco (Universidad de Concepción, Barrio Universitario, Chile), Loretta Dunne (Department of Physics and Astronomy, University of Canterbury, New Zealand; Institute for Astronomy, University of Edinburgh, Royal Observatory, UK), Stephen Eales (School of Physics and Astronomy, Cardiff University,UK) , Simone Fleuren (School of Mathematical Sciences, University of London, UK), Roxana E. Lupu (Department of Physics and Astronomy, University of Pennsylvania, USA), Steve J. Maddox (Department of Physics and Astronomy, University of Canterbury, New Zealand; Institute for Astronomy, University of Edinburgh, Royal Observatory, UK), Michał J. Michałowski (Institute for Astronomy, University of Edinburgh, Royal Observatory, UK), Alain Omont (Institut d'Astrophysique de Paris, UPMC Univ. Paris, France), Kate Rowlands (School of Physics & Astronomy, University of St Andrews, UK), Dan Smith (Centre for Astrophysics Research, Science & Technology Research Institute, University of Hertfordshire, UK), Matt Smith (School of Physics and Astronomy, Cardiff University,UK) and Elisabetta Valiante (School of Physics and Astronomy, Cardiff University, UK)
* Images of Hubble: http://www.spacetelescope.org/images/archive/category/spacecraft/
* ESO press release: http://www.eso.org/public/news/eso1426/
* Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1426/eso1426a.pdf
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