1994A&AS..107..563B

Result. are presented from an absorption line survey of the galactic centre region in the OH main lines (frequencies 1667.359MHz and 1665.402MHz). The survey was made using the 250ft Lovell Telescope at Jodrell Bank which has a beamwidth of 10 arcmin at these frequencies. Spectra were taken on a grid with 0.2deg spacing. The entire region between 354deg≤l≤8.6deg and -1.0deg≤b≤+1.0deg was surveyed with extensions out to b=-2.0deg and b=+1.6deg at some longitudes. The spectra were taken using an autocorrelation spectrometer with spectral bandwidth 5MHz, a velocity range of 900km/s and a resolution of 3.1km/s. The rms noise level achieved was typically 80-90mK. The data are presented as a series of longitude-velocity (l-V), latitude-velocity (b-V) and longitude-latitude (l-b) contour maps of line temperature and apparent opacity. The survey reveals that the molecular gas in the galactic centre is much more extensive than previously thought. The molecular nuclear disk can be traced over the entire region 354deg<l<6deg, a projected size of ∼1.8kpc. The disk appears to be warped, lying preferentially to positive latitudes at negative longitudes and negative latitudes at positive longitudes. The gas reaches latitudes of ±1.6deg, corresponding to z-distances of ±240pc out of the galactic plane. The new features are described in detail. There are 7 broadline "clumps"; concentrations of molecular gas with angular sizes typically 0.6deg and large velocity extents of typically 200km/s. The clumps have positive gradients of velocity with galactic longitude. Some of the clumps appear to be connected by narrow filaments which have velocity widths of typically 30km/s. There are also a number of molecular spur features which extend outwards from the nucleus to latitudes of ±1.0.deg These appear to be associated with radio continuum features, including the galactic centre lobe.