18-cm VLA observations of OH towards the Galactic Centre^*

Absorption and emission in the four ground-state OH lines

¹ Stockholm Observatory, SCFAB-AlbaNova, 106 91 Stockholm, Sweden e-mail: rolandk@astro.su.se
² Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ NRAO Array Operations Center, PO Box 0, Socorro NM 87801, USA e-mail: lsjouwer@aoc.nrao.edu
⁴ CSIRO, Australian Telescope National Facility, Box 76, Epping NSW 2121, Australia e-mail: jwhiteoa@atnf.csiro.au

Corresponding author: Aa. Sandqvist, aage@astro.su.se

Received: 8 July 2002
Accepted: 28 February 2003

Abstract

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. Maps are presented with a channel velocity resolution of about 9 km s^-1 and with angular resolutions of . Some clear results are highlighted here, such as absorption from the Circumnuclear Disk (CND) and the OH-Streamer inside the CND near Sgr , strong absorption towards most of the eastern and western parts of the Sgr A East shell, lack of absorption towards both Sgr A West and the compact H ii-regions to the east of Sgr A East, and double-lobed structure of the High Negative Velocity Gas (HNVG) oriented northeast and southwest of Sgr , and finally compact, point-like maser emission in all four transitions, in particular a 1720-MHz maser at -132 km s^-1 in the CND as counterpart to a 1720-MHz maser at +132 km s^-1 in the CND.