Quasar absorption lines

Studies of diffuse gas at cosmological distances have been performed by analysing the UV spectra of quasars and deep high resolution images of quasar fields obtained with the Hubble Space Telescope spectra. These data have revealed that large amounts of gas may be associated with various galaxy types, and not only with luminous spirals.

The analysis of metal abundances and dust or molecular content in the highest column density systems strongly suggests that quasar absorption line data are biased towards low metallicity, dust and H2 free gas and do not provide a representative view of the interstellar medium in distant galaxies (P. Boissé in collaboration with J. Bergeron (ESO, Munich), V. Le Brun and J.M. Deharveng (LAS, Marseille). Studies of fainter quasars with the Very Large Telescope (VLT) are planned to overcome the present limitations.

Another short-term VLT project designed to get a good characterisation of the three-dimensional structure of the tenuous intergalactic gas by observing multiple quasar lines of sight is also in progress (collaboration with the team headed by P. Petitjean (IAP, Paris)).