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Cymraeg

Revealing hidden galaxies

04 November 2010

Gravitational lensing illustrationImage illustrates the effect of gravitational lensing as seen by Herschel and ground-based telescopes. View large image with caption

A new way of exploring hidden galaxies in the early Universe has been discovered by an international team including astronomers from Cardiff University.

Using the European Space Agency’s Herschel Space Observatory, the team have used a natural space phenomenon - which acts like a zoom lens – to allow astronomers to peer at galaxies in the distant and early universe.

These results were found as part of the largest imaging survey so far on Herschel – the largest space telescope of its kind.

Professor Steve Eales, School of Physics and Astronomy, joint leader of the survey, said: "We have discovered a relatively simple technique which will enable us to unlock the secrets of galaxies hidden from optical telescopes. And this is only the tip of the iceberg."

It was Albert Einstein who first showed that gravity can cause light to bend. The effect is normally extremely small - it is only when light passes close to a very large object such as a galaxy containing hundreds of billions of stars that the results become easily noticeable.

When light from a very distant object passes a galaxy much closer to us, its path can be bent in such a way that the image of the distant galaxy is magnified and distorted. These alignment events - known as gravitational lenses - have been discovered over recent decades, mainly at visible and radio wavelengths.

Previous methods of searching for gravitational lenses have been relatively inefficient. However, Herschel is able to look at far-infrared light, which is emitted not by stars, but by the gas and dust from which they form. Combined with its panoramic imaging cameras, astronomers are now able to find examples of these lenses by scanning large areas of the sky in far-infrared and sub-millimetre light.

Dr Mattia Negrello from the Open University and lead researcher of the study said: We’ve discovered that these cosmic zoom lenses are at work in not just a few, but in all of the distant and bright galaxies seen by Herschel.

"We no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths."

The new images taken by Herschel are part of the "Herschel-ATLAS" survey, and contain thousands of galaxies, most so far away that the light has taken billions of years to reach us.

Using Herschel, the team investigated five surprisingly bright objects in this small patch of sky. Looking at the positions of these bright objects with optical telescopes on the Earth, they found galaxies that would not normally be bright at the far-infrared wavelengths observed by Herschel. This led them to suspect that the galaxies seen in visible light might be gravitational lenses magnifying much more distant galaxies seen by Herschel.

To find the true distances to the Herschel sources, the team looked for a tell-tale signature of molecular gas, they showed that this signature implies the galaxies are being seen as they were when the Universe was just 2–4 billion years old – less than a third of its current age. The galaxies seen by the optical telescopes are much closer, each ideally positioned to create a gravitational lens.

Herschel

The magnification provided by these cosmic zoom lenses allows astronomers to study much fainter galaxies, and in more detail than would otherwise be possible. They are the key to understanding how the building blocks of the Universe have changed since they were in their infancy.

Professor Eales, School of Physics and Astronomy, said: "80% of the matter in the Universe is thought to be dark matter, which does not absorb, reflect or emit light and so can’t be seen directly with our telescopes. We’re finding so many cosmic zoom lenses in our survey, we will really be able to get to grips with this hidden Universe."

None of the results would have been possible without the performance capabilities of the Herschel space observatory. One of Herschel's three instruments, called SPIRE, was developed be an international consoritium led by Professor Matt Griffin.

Professor Griffin, School of Physics and Astronomy, said: "We are continually being surprised by the results from SPIRE. We’ve gone from the discovery of water where it shouldn't really exist in our galaxy to studying the infant Universe. Now we will be able to use Herschel to study these very distant galaxies as though they were much closer. These results highlight the power of Herschel to reveal the dark side of the Universe."

Dr Simon Dye, School of Physics and Astronomy, and part of the team that created the Herschel-ATLAS images and co-author of the study said: "Herschel's instruments are incredible. They survived a gruelling launch and a long journey to the telescope's observing point at 1.5 million kilometres away from Earth, and yet the quality of data they are returning is as good as the quality measured in the lab. I feel privileged to be given the opportunity to work with this dataset."