Observations of OH in the Galactic Centre

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Abstract
Observations of the 1665- and 1667-MHz ground state lines of OH in the galactic centre region have been made using the J odrell Bank Mk IA telescope (beam 11ʹ). A5-MHz bandwidth was used, covering both lines simultaneously with a velocity resolution of 6·1 km s–1. The data are presented as contour maps of antenna temperature as a function of galactic longitude and velocity, and as a function of latitude and velocity. Similar maps of apparent opacity are also given. Line saturation effects are observed in a large number of clouds. The optical depths deduced from line ratios and line broadening are typically an order of magnitude greater than the apparent optical depths. The derived optical depths also show no tendency to decrease at negative longitude, whereas the apparent optical depths fall sharply. Several new OH clouds are found at positions and velocities corresponding to the H I nuclear disk feature. All other high-velocity OH clouds detected in the present observations also have counterparts in H I. Possible evidence of explosive events in the galactic nucleus and possible evidence of a central bar are discussed.

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