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The "Galaxy" team
of the Astrophysics Laboratory (CNRS - Université de Toulouse 3)
of the Midi-Pyrénées Observatory has recently succeeded
in obtaining multiple wavelength data on two distant galaxies, «S2
and A2» (z ~ 1.9) , ten times fainter than those
studied up until now. This is the first time that such high-quality observations
have been obtained for such faint and distant galaxies. These observations
have made it possible to determine the physical properties of these galaxies
with unprecedented precision, at a time when the universe was only several
billion years old. These results shed new light on the "young"
universe and provide us with a better understanding of how galaxies are
formed and evolve over time.
These observations were made possible thanks to a "gravitational
telescope" in which a galaxy cluster, known as AC114, acts as a magnifying
glass for more distant galaxies. On the basis of ultraviolet and visible
spectrums (object rest-frame) obtained with spectrographs FORS1 and ISAAC,
respectively, of the Very Large Telescope (ESO) located on Mount Paranal
in Chile, this team explicitly determined the physical properties of these
very young galaxies, such as their star formation rate, their metallicity
and their mass, by using the same indicators used for galaxies in the
local universe. This is the first time that this technique could be applied
to such faint and distant galaxies. Although these two galaxies are very
close to each other in space, their physical properties are very different.
For example, S2 is very poor in heavy elements whereas A2 has a chemical
enrichment level comparable to the most massive spiral galaxies in the
near universe. This difference in chemical abundance implies obvious differences
in the evolutionary process of these two galaxies. A2 has already undergone
several major episodes of star formation whereas S2 appears to be much
younger. Thanks to gravitational amplification and the excellent quality
of data, it was possible to determine the velocity gradient of the S2
galaxy for the first time for such a faint and distant galaxy. This research
enables the precise determination of the mass of the galaxy which is ten
times less than our own. These data are absolutely necessary to understanding
the processes underlying galaxy formation.
These results emphasize the importance of a multiple wavelength approach
in the study of the evolution of galaxy properties. Such groundbreaking
studies are a necessary stage in the preparation of large-scale observation
projects on big telescopes such as the "VIRMOS/VLT Deep Survey"
and the COSMOS/EMIR project on the Grantecan, a 10-meter telescope that
was recently built in the Canary Islands. One of the main goals of these
projects is to determine the physical properties of several thousand very
distant galaxies.
This project was carried out thanks to funding by the CNRS, through a
joint Franco-Chilean research program, "ECOS-Sud" (ECOS/CONICYT
CU00U05), and the Regional Council of Martinique, through the funding
of a research grant.
Note
:
Z , commonly
referred to as "redshift", measures the distance of a galaxy
in relation to the earth. The higher the redshift value, the more distant
the galaxy. A redshift on the scale of 2 corresponds to a time when the
universe was only several billion years old, based on the assumption that
the universe is 15 billion years old. The redshift of very distant objects
is an optical effect related to the expansion of the universe. During
the time that light from these galaxies, located at the edge of the universe,
was making the long trip to our telescopes, the universe had the time
to considerably increase its volume. This had the effect of lengthening
the wavelength of light and making it appear redder.
Publication:
"Physical Properties of two low-luminosity z ~ 1.9 galaxies behind
the lensing cluster AC 114"
M. Lemoine-Busserolle, T. Contini, R. Pello, J.-F. Le Borgne, J.-P. Kneib
& C. Lidman
To be published in Astronomy & Astrophysics
Article available at: http://fr.arxiv.org/abs/astro-ph/0210547
Team:
Marie Lemoine-Busserolle, Thierry Contini, Roser Pello, Jean-Francois
Le Borgne
& Jean-Paul Kneib:
"Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées"
(CNRS - Université de Toulouse 3), Toulouse - France
Cris Lidman: European Southern Observatory, Vitacura - Chile
Researcher
contact:
Thierry Contini
Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées
(CNRS - Université de Toulouse 3)
Tel: +33 5 61 33 28 14
e-mail: contini@ast.obs-mip.fr
Press contacts:
Dominique d'Arabian
Public Relations Manager
Observatoire Midi-Pyrénées
Tel: +33 5 61 33 28 67
e-mail: domid@obs-mip.fr
Carine Noël
Tel : +33 1 44 96 49 88
e-mail : carine.noel@cnrs-dir.fr
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