A LARGE-SCALE SURVEY OF OH IN THE GALACTIC-CENTER

Results are presented from an absorption line survey of the galactic c entre region in the OH main lines (frequencies 1667.359 MHz and 1665.4 02 MHz). The survey was made using the 250ft Lovell Telescope at Jodre ll Bank which has a beamwidth of 10 arcmin at these frequencies. Spect ra were taken on a grid with 0 degrees.2 spacing. The entire region be tween 354 degrees less than or equal to l less than or equal to 8 degr ees.6 and -1 degrees.0 less than or equal to b less than or equal to+1 degrees.0 was surveyed with extensions out to b = -2 degrees.0 and b = +1 degrees.6 at some longitudes. The spectra were taken using an aut ocorrelation spectrometer with spectral bandwidth 5 MHz, a velocity ra nge of 900 km s(-1) and a resolution of 3.1 km s(-1). The rms noise le vel achieved was typically 80-90 mK. The data are presented as a serie s of longitude-velocity (l-V), latitude-velocity (b-V) and longitude-l atitude (l-b) contour maps of line temperature and apparent opacity. T he survey reveals that the molecular gas in the galactic centre is muc h more extensive than previously thought. The molecular nuclear disk c an be traced over the entire region 354 degrees<1 <6 degrees, a projec ted size of similar to 1.8 kpc. The disk appears to be warped, lying p referentially to positive latitudes at negative longitudes and negativ e latitudes at positive longitudes. The gas reaches latitudes of +1 de grees 6, corresponding to z-distances of +/-240 pc out of the galactic plane. The new features are described in detail. There are 7 broadlin e ''clumps''; concentrations of molecular gas with angular sizes typic ally 0 degrees.6 and large velocity extents of typically 200 kms(-1). 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 30 kms(-1). There are also a number of molecular spur features which extend outwards from the nucleus to l atitudes of +/-1 degrees.0. These appear to be associated with radio c ontinuum features, including the galactic centre lobe.