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A (Less)er Challenge To Galaxy Formation

April 22, 2009

An international team of astronomers have undertaken a survey with a new submillimeter camera have discovered more than a hundred dusty galaxies in the early Universe, each of which is in the throes of an intense burst of star formation. One of these galaxies is an example of a rare class of starburst, seen just 1 billion years after the Big Bang. In her presentation on Wednesday 22nd April at the European Week of Astronomy and Space Science conference, team leader Dr. Kristen Coppin of Durham University will discuss the new results and how they may present a direct challenge to our current ideas of how galaxies formed.

The team (known as the LESS collaboration) used the new Large Apex Bolometer Camera (LABOCA) camera on the Atacama Pathfinder Experiment (APEX) telescope sited in the Atacama Desert in Chile to make a map of the distant galaxies in a region of the sky called the Extended Chandra Deep Field South.  These galaxies are so far away that we see them as they appeared billions of years ago. LABOCA is sensitive to light at wavelengths just below 1mm (submillimeter radiation), and is able to find very dusty and very luminous galaxies at very early times in the history of the Universe. These submillimeter galaxies represent massive bursts of star formation associated with the early formation of some of the most massive galaxies in the present-day Universe: giant elliptical galaxies.

For many years it has been thought that these giant elliptical galaxies formed most of their stars at very early times in the Universe, within the first billion years after the Big Bang. However, very few examples of these very distant and very bright dusty sources have been found in submillimeter surveys, until the LESS collaboration completed their survey of a Full Moon-sized patch of sky in the southern hemisphere constellation of Fornax.  Their survey is the largest and deepest of its kind in submillimeter radiation and reveals over a hundred galaxies that are forming stars at a prodigious rate.

Working with their new map, the team identified one of the submillimeter sources as being associated with a star forming galaxy which is seen just 1 billion years after the Big Bang. This remarkable galaxy shows the signatures of both intense star formation and obscured black hole growth when the Universe was only 10 percent of its current age. Dr. Coppin and the LESS team suggest that there could be far more submillimeter galaxies lurking at these early times than had previously been thought.  Dr Coppin comments, “The discovery of a larger number of such active galaxies at such an early time would be at odds with current galaxy formation models”.

Image Caption: The image shows the most distant submillimeter galaxy discovered by the LESS collaboration. The main image shows a wide 3-color optical image from the NASA/ESA Hubble Space Telescope (HST), overlaid by the contour map from the LESS survey made using the LABOCA submillimeter camera. Higher resolution radio and NASA Spitzer Space Telescope mid-infrared data have pinpointed the source of the submillimeter emission to the optical galaxy indicated by a box. The observed energy output of the galaxy measured as a function of wavelength is plotted in the inset, showing that most of the energy is being emitted in the far-infrared and submillimeter from dust-reprocessed starlight. Using spectroscopic data from the Keck telescope on Hawaii and the ESO VLT in Chile, the light travel time to the object is 12 billion years, meaning we are seeing it as it was just over 1 billion years after the Big Bang. Credit: K. Coppin / the LESS collaboration

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