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Gas masses derived for the bulge regions of the Milky Way and the nearby starburst galaxy NGC 253 using the C18O rotational lines are 5-10 times lower than those from 12CO and a standard X. Also, the distributions of both isotopomers differ. It is suggested that due to the stellar potential, 12CO arises in part from optically thin intercloud gas.

We have identified the gas affected by the explosion that created Sgr A East (Sgr A East Core) and show that M-0.13-0.08, the CND and Sgr A East Core — the main molecular features within the 10′ of the Galactic Centre — are physically connected.

Chemical properties of extragalactic molecular clouds are summarized. Column densities, relative abundances, and chemical implications are briefly discussed and references for more detailed studies are given. The need for model calculations is emphasized.

To use a molecule as a diagnostic of a single star forming region, one has to observe it in different transitions. That is especially true for galaxies, where the beam filling factor is small and unknown. From studies of Galactic objects, the CS molecule is a good tracer of dense gas. Toward the IR galaxies NGC 253, IC 342 and M 82, Mauersberger and Henkel (1989) observed the J=2—1, 3=—2 and 5—4 transitions of CS at 3, 2 and 1.3 mm wavelength, repectively. They also measured emission of the isotope C34S, which has an abundance ~ 1/23 that of the main isotope. This study revealed that the H2 densities in the circumnuclear gas exceed 104, and, in the case of NGC 253, 105 cm-3. In all three cases, the distribution of the dense gas traced out by CS follows the CO distribution

We have recently discovered a large-scale (200”) outflow system in the core of OMC-1 (fig. 1), centered about 100” South of IRc2 and extending over some 120” (red lobe) resp. 60” (blue) along a position angle of —31°Schmid-Burgk et al. 1990). The blue lobe which might actually trude into the Ell region M42is poorly defined in CO 2-1, but the red lobe reveals a number of remarkable properties which we summarize here