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The VLT Reaches Out Towards the Horizon

FORS Spectra of Very Distant Quasars

27 de Febrero de 1999

The FORS1 multi-mode instrument is able to record images as well as spectra of even very distant objects. During the past months, data have been obtained that show the properties of some of the remotest known objects in the Universe.

Three spectral tracings of very distant quasars are shown here. They were obtained by the FORS Commissioning Team in September and December 1998 in the long-slit spectroscopy mode of FORS1. This instrument is very efficient; even for the most distant and faintest quasar, the exposure time was only 1 hour.

The redshifts z of these quasars are larger than 3. The wavelength of the emitted light is therefore received at wavelengths that are larger (longer) by factors of more than 4 than the rest wavelength (i.e. at the quasar). In each of the diagrammes, the redshift z of the object and the (smaller) redshifts of some tentatively identified absorption lines are indicated. These absorption lines are formed in gas clouds that are located along the line of sight between the quasars and us.

One of the objects observed, "Quasar 1" has a redshift of no less than 5.0. It was discovered by X. Fan et al. within the Sloan Digital Sky Survey Collaboration and is one of the most distant objects known at present. Its light was emitted when the age of the Universe was only a few percent of its present value.

When studied in detail, these high-quality FORS spectra will provide accurate information on the chemical composition of the gas in these remote objects.

All three spectra were obtained in the long-slit spectroscopy mode of FORS1. The total exposure times were only 30 min for Q0103-294, 20 min for Q0046-282, and 60 min for "Quasar 1".

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