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Claire de Thoisy-Méchin

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Tel. +33 (0)1 44 27 23 34

Email: claire.de_thoisy-mechin@upmc.fr

 

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Katherine Tyrka

International Press Relations

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Email: katherine.tyrka@upmc.fr

A giant elliptical galaxy detected in the early Universe

An international team of astronomers led by researchers at the CEANouvelle fenêtre, with teams from the CNRS Nouvelle fenêtreand universities (UPMC, Paris Diderot UniversityNouvelle fenêtre, University of ProvenceNouvelle fenêtre), detected for the first time in the early Universe a giant elliptical galaxy, very similar to its cousins in our local Universe. This galaxy, located 10.1 billion light years from Earth, has been observed at a point when the Universe was only 3.6 billion years old. This discovery shows that some elliptical galaxies can reach their "adult" size early in the evolution of the Universe. They coexist with other much smaller elliptical galaxies which increase in size over time. These results are published in the Astrophysical Journal LettersNouvelle fenêtre.

 

Researchers analyze the light coming from very distant galaxies to clarify the mysteries of the distant past of our Universe. The elliptical galaxies are of particular concern to astronomers. These regions give rise to many questions. In fact, elliptical galaxies are not the seat of important star formation so they should have a relatively narrow evolution over time. However, some years ago, images of the distant Universe, taken by the Hubble Space Telescope, suggest that distant elliptical galaxies could be two to five times smaller than their counterparts of similar mass in the local Universe. To reach their "adult" size elliptical galaxies would be forced to boost their volume, which contradicts the theory.

"We wanted to find any giant elliptical galaxy in the early Universe," said Masato Onodera, researcher at the CEA. "We used the velocity dispersion of stars technique to 'weigh' distant galaxies. As the size of a galaxy of a given mass is smaller, the stars constituting it must quickly turn around the galactic center to compensate the gravitational attraction," he adds.

To gain access to these valuable data, researchers have turned to one of the greatest records of the early Universe, the COSMOS project. They looked for objects with specific spectral signatures in the visible and near infrared, as those detected by the camera Suprime-Cam of the Subaru telescope and camera WIRCam of the Canada-France-Hawaii telescope. Then they used the Subaru telescope equipped with a spectrographer and an infrared camera in multi-object reached the infrared spectra of the studied distant galaxies. The analysis of the widening of spectral lines allows researchers to go back to the mass and size of the studied galaxies.

They were able to detect a giant elliptical galaxy located 10.1 billion light years away from Earth and observed when the Universe was only 3.6 billion years old. This result provides evidence that massive galaxies coexist with other, more compact ones, once they reach their adult stage in the early Universe. Furthermore, this study brings an additional piece to the puzzle for understanding the evolution of elliptical galaxies. Researchers are now getting down to quantifying the relative proportion of these two extreme types of elliptical galaxies, depending on the cosmic time.



26/05/10