IV - STRUCTURE A GRANDE ÉCHELLE
CARBON MONOXIDE IN THE GALACTIC DISK AND NUCLEUS

Résumé
Le gaz interstellaire de notre galaxie est concentré en nuages denses et optiquement épais où l'hydrogène est principalement moléculaire. D'après les observations de la transition J = 1 → 0 de CO, la plupart de ces nuages se trouve dans un anneau de 4 à 8 kpc du centre galactique. Leur distribution spatiale ressemble à celle des étoiles jeunes, des supernovae, des pulsars, etc. et diffère de la distribution du gaz diffus et essentiellement atomique. Dans un rayon de 1 kpc du centre galactique, on observe du gaz moléculaire à grande vitesse (relative au centre), incliné par rapport au plan galactique.

Abstract
Most of the interstellar gas in our Galaxy is concentrated in dense, optically opaque clouds in which hydrogen is principally molecular. As traced in the J = 1 → 0 rotational transition of CO, these clouds are found to lie mostly in an annulus between 4 and 8 kpc from the galactic centre, and to have a spatial distribution similar to that of young stars, supernovae, pulsars, etc. This distribution is, however, quite different from that of the more diffuse gas in which hydrogen is principally atomic. In the innermost kpc of the Galaxy, there is a prominent component of molecular gas having a large velocity with respect to the galactic centre. This gas has a spatial distribution which is tilted with respect to the fundamental plane of the larger-scale galactic morphology.