The most distant galaxy ever measured
1er octobre 2010
The distance of the most remote galaxy in the Universe has just been measured, by a European team of astronomers, led by a researcher from Paris Observatory. They used the Very Large Telescope (VLT) of ESO and its spectrograph SINFONI, to detect the Lyman-alpha line of hydrogen, and thus measure its redshift of z=8.5549. The Universe was only 600 million years old, when the galaxy sent these photons to us. These are the first confirmed observations of a galaxy in the reionisation epoch, when the Universe still contained diffuse and opaque neutral hydrogen between the galaxies. These results were published Thursday October 21 in Nature.
See the ESO press release The study of these first galaxies is extremely difficult. Even if their initial luminosity is high, viewed from the Earth they seem very weak and small. Moreover, this weak light falls most of the time into the infra-red part of the spectrum because its wavelength was redshifted by the expansion of the universe. In addition, at these early times, less than one billion years after the Big Bang, the Universe was not entirely transparent and a great part was filled of hydrogen fog which absorbs the UV light of the young galaxies. Indeed, the first galaxies do reionize the intergalactic space, and during this period, called the epoch of reionization, the Universe includes patches of ionized hydrogen in a continuum of opaque neutral hydrogen. In spite of these challenges, the new wide field camera on the Hubble Space Telescope discovered in 2009 several objects, candidates to be the most remote galaxies. The confirmation of the distances from such weak objects is an enormous challenge which can only be addressed by the spectroscopy on large ground-based telescopes, by measuring the redshift of the light of the galaxy. A Franco-British team, led by a researcher from Paris Observatory, made a special request to the director-general of ESO and obtained telescope time on the VLT to observe a candidate galaxy called UDFy-38135539 during 16 hours. After two months of very careful analysis and tests of their results, the team noted that they had clearly detected the very weak hydrogen line redshifted to z= 8.6, which makes this galaxy the most distant object ever confirmed by spectroscopy. A redshift z=8.6 corresponds to a galaxy seen just 600 million years after Big Bang.
- Figure 1 : Image en raie Lyman-alpha de la source UDFy-38135539. L’encart montre la réponse de l’instrument à une source ponctuelle (PSF). L’échelle de grisé montre le rapport signal-à-bruit. L’image est compatible avec une source ponctuelle, compte-tenu de la turbulence de l’atmosphère.
The detection of this weak luminosity in Lyman-alpha shows that this galaxy is not sufficient to have reionized the Universe around it. There must be other galaxies, probably weaker, less massive and close to this galaxy, which also helped to make space transparent around it.
- Figure 2 : Deux représentations du spectre de la source. L’image du haut montre la raie de Lyman-alpha de l’hydrogène, décalée de z=8.5549. L’image du bas montre le spectre à 2 dimensions, avec la longueur d’onde en abscisse, et la coordonnée d’ascension droite en ordonnée. La source est indiquée par le cercle blanc. Les perturbations du ciel nocturne sont visibles dans le reste de l’image. Cliquer sur l’image pour l’agrandir
At the limit of capacity of the current telescopes, this type of scientific problems could be fully approached with the very large instruments of the future, i.e. the European Extremely Large Telescope (E-ELT), the James Webb Space Telescope (JWST), or the large millimetre interferometer ALMA (Atacama Large Millimeter Array).
Reference Spectroscopic confirmation of a galaxy at redshift z=8.6 M. D. Lehnert (Obs-Paris), N. P. H. Nesvadba (IAS-Orsay), J.-G. Cuby (Marseille), A.M. Swinbank (Durham, UK), S. Morris (Durham, UK), B. Clément (Marseille), C. J. Evans (Edinburgh, UK), M. N. Bremer (Bristol, UK) & S. Basa (Marseille) Nature, Thursday 21 October 2010 Contact Matt Lehnert (Observatoire de Paris, GEPI et CNRS)
Dernière modification le 4 mars 2013