The overall distribution of carbon monoxide in the plane of the Galaxy

The 2.6-mm line of $sup 12$CO is observed at 5degree longitude intervals along the galactic equator between l=10degree and 200degree with a velocity coverage sufficient to include all velocities expected in terms of differential galactic rotation. CO emission is generally observed at positive velocities (LSR) at l 8 kpc and R R$sub 0$=10 kpc, only a few isolated emission peaks are found, generally associated with known H ii regions. Histograms of abundance as a function of R are given for the distributed CO and H i, and for giant H ii regions. H ii and CO show amore » rather similar large-scale distribution (although that of the H ii is less regular); both are more concentrated than H i to the inner Galaxy as well as more concentrated than H i to the galactic plane. Similar morphological characteristics also distinguish the distribution of OH, supernova remnants, very young stars, pulsars, $gamma$-radiation, and diffuse H ii gas from that of the neutral hydrogen. The relative distributions are amenable to interpretation in terms of compression on a galactic scale associated with density-waves. (AIP)« less