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Paris, March 8, 2006
Discovery of the missing link in the menagerie of distant galaxies
A new type of galaxy has just been discovered by an international team of researchers (1) led by Denis Burgarella of the Laboratoire d'astrophysique de Marseille (LAM - Marseille Astrophysics Laboratory) (CNRS/Université de Provence). This represents a genuine missing link in the menagerie of distant galaxies, and enables a clear link to be established between populations of galaxies which until now appeared to be unconnected. Unexpectedly, the vast majority are spiral galaxies similar to those in our own local universe. This discovery, which will shortly be published in Astronomy & Astrophysics, has given us valuable information about the evolution of galaxies like our own, the Milky Way.
Over the last ten years or so, observations of the distant Universe have enabled astronomers to detect two major families of galaxies where stars are formed in huge numbers (2) : on the one hand, galaxies where hot, young stars emit photons, which can be directly observed at ultraviolet and visible wavelengths and, on the other hand, galaxies whose young stars are concealed within cocoons of dust, and which can only be seen at infrared and submillimeter wavelengths.
No family of galaxies lying in between these two categories had ever previously been detected. However, finding a link between the two could enable astrophysicists to find out more about galaxy formation and evolution. Do ultraviolet galaxies eventually turn into infrared galaxies (or vice-versa), or alternatively do they follow two parallel but separate paths?
To attempt to answer these questions, Denis Burgarella's team used data obtained from two space telescopes, one which makes observations in the ultraviolet (GALEX, a NASA satellite, which LAM was involved in developing), and the other in the infrared (NASA's Spitzer/MIPS), as well as data obtained from one of the telescopes at the European Southern Observatory (ESO), which uses visible wavelengths.
The study was carried out on 300 ultraviolet galaxies in the distant Universe (3), selected on the basis of GALEX data. The big surprise was that, thanks to SPITZER, some of these galaxies were detected for the first time in the infrared. This was how a population of galaxies, which has the properties of both major families of galaxies with high star formation rates in the distant Universe, was finally discovered.
The images from the Hubble space telescope (GOODS project) also revealed that the vast majority of these galaxies are spiral galaxies similar to those found in the local Universe. This discovery by Denis Burgarella and his team makes it possible to calculate with unprecedented accuracy the number of stars which form in the Universe at different times, and to improve our understanding of the origin of large spiral galaxies such as the Milky Way.
© NASA, ESA, GOODS team. Montage of six images of galaxies observed by Denis Burgarella and his team, located over 6 billion light years away in the distant Universe. The first five galaxies are spiral galaxies. The structure of the last one shown is more irregular, probably due to interaction with neighboring galaxies.
Notes:
(1) The team is made up of French, American, Japanese and Korean researchers : D. Burgarella, P. G. Perez-Gonzalez, K. D. Tyler, G. H. Rieke, V. Buat, T. T. Takeuchi, S. Lauger, S. Arnouts, O. Ilbert, T. A. Barlow, L. Bianchi, Y.-W. Lee, B. F. Madore, R. F. Malina, A. S. Szalay, S. K. Yi
(2) As many as several hundred stars per year, as compared to just a few per year in the Milky Way.
(3) At a time when the Universe was less than half its current age.
Contact information:
Researcher
Denis Burgarella
T 04 91 05 69 71
denis.burgarella@oamp.fr
INSU
Philippe Chauvin
T 01 44 96 43 36
Philippe.chauvin@cnrs-dir.fr
Press
Delphine Kaczmarek
T 01 44 96 51 37
Delphine.kaczmarek@cnrs-dir.fr
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