Molecular gas at large and medium redshifts: physical conditions,
chemical composition and isotopic abundances
Michel GUELIN
IRAM/LRA-ENS/LERMA.
Résumé :
Observation of mm-wave molecular lines at large/meduim redshifts is a
powerful tool for the study of interstellar matter in the young
Universe. I will review the latest results obtained with the IRAM
Plateau de Bure interferometer, more particularly those dealing with
molecules larger than CO. A dozen of molecular species --and a score of
isotopologues of those species-- have been detected in absorption in the
disks of two spirals of redshift 0.7-0.9, enabling us to measure the
elemental isotopic ratios of C, H, O, N and S in the interstellar gas
and to constrain the star formation history in these objects. The
absorption profiles observed in one galaxy show drastic variations on
time scales of a few years; those variations teach us about the
structure of the clouds causing the absorption.
For the time being, the number of molecular species detectable in high
redshift galaxies is severely limited by lack of sensitivity. However,
in a decade, the fully operational ALMA will make it possible to observe
many more species and objects, enabling us to follow the chemical
evolution of galaxies throughout the Universe. In the mean time, project
NOEMA, which will allow to simultaneously observe with an upgraded
Plateau de Bure interferometer all spectral lines within a 32-GHz wide
band, will provide enough gain in sensitivity to embark into such a study.
