Quasars are extremely bright nuclei of distant galaxies. Due to their high luminosity they constitute unique cosmological probes. The light emitted by the quasar is absorbed by the intervening gas clouds. The observation and interpretation of absorption lines in quasar spectra has become one of the major topics in cosmology, since it provides valuable information about the cmposition, distribution and evolution of matter in the Universe.
The number of suitable quasars to be used as background sources is at present rather small, since, unfortunately, the light from bright quasars is often totally absorbed. The Hamburg group has discovered bright high-redshifted quasars adequate for detailed absorption study from observations gained with large gground-based telescopes and also with the Hubble Space Telescope (HST). The work on the quasar HS 1700-6416 (e.g. Vogel and Reimers 1995, A and A 294,377) has shown that plenty of precious information can be obtained by studying simultaneously ultraviolet and optical spectra. The analysis of the spectra of the bright (V=16.5) high-redshift (z = 2.4) quasar HE 1122- 1649 is the purpose of this project.
Ultraviolet data of HE 1122-1649 have been quite recently obtained with the Faint Ojbect Spectorgraph onboard the HST and optiacl data with CASPEC at the 3.6m telescope at ESO/La Silla. The analysis of the absorption spectra allow the study of distant galaxies and of rather unevolved gas clouds which are otherwise not detectable. New results concerning the properties of the absorbing gas clouds (chemical enrichement, ionization and thermal state, distribution and evolution, confinement, etc.) and the intergalactic radiation field at high redshift are expected.