Absorption and Emission in the Four Ground-State OH Lines Observed with the VLA Towards the Galactic Centre

R. Karlsson1, Aa. Sandqvist1, L. O. Sjouwerman2 and J. B. Whiteoak3

1 Stockholm Observatory, SCFAB-AlbaNova, SE-106 91 Stockholm, Sweden
2 NRAO Array Operations Center, P.O. Box 0, Socorro NM 87801, USA
3 CSIRO, Australian Telescope National Facility, Box 76, Epping NSW 2121, Australia

E-mail contact: rolandk@astro.su.se, aage@astro.su.se

The OH distribution in the Sgr A Complex has been observed in the 1612-, 1665-, 1667- and 1720-MHz OH transitions with the Very Large Array (VLA) in BnA configuration and in the 1665- and 1667-MHz OH transitions with the VLA in DnC configuration. Some clear results are highlighted here, such as absorption from the Circumnuclear Disk (CND) and the OH Streamer inside the CND near Sgr A*, strong absorption towards both the eastern and western parts of the Sgr A East shell, lack of absorption towards both Sgr A West and the compact HII-regions to the east of Sgr A East, and double-lobed structure of the High Negative Velocity Gas (HNVG) towards the CND oriented northeast and southwest of Sgr A West, and finally compact, point-like maser emission in all four transitions, in particular a 1720-MHz maser at -132 kms-1 in the CND as counterpart to a 1720-MHz maser at +132kms-1 in the CND. Special emphasis is placed on analysis of the OH Streamer.