The 18-cm OH distribution in the Galactic Center Torus

Abstract

The 18‐cm OH distribution in the Galactic Center region near Sgr A has been studied in all four of the 1612, 1665, 1667 and 1720 MHz OH lines using the VLA with 4 arcsec angular resolution and 9 km s−1 velocity resolution. Three 1667 MHz OH spectral line absorption maps, at +51, +25 and −1 km s−1, covering a 4’.3×4’.3 region around Sgr A are presented together with an 18‐cm continuum map. In addition, a complete set of velocity maps from +139 to −159 km s−1, covering a 3’×3’ region around the Galactic Center nuclear torus, is presented. Absorption by the +50 and +20 km s−1 molecular cloud belt is seen towards Sgr A East, but not towards Sgr A West. Absorption is also seen towards Sgr A* in the velocity ranges of +43 to −36 km s−1 and −142 to −151 km s−1. The Northeast and Southwest torus components can be traced out to velocities of +139 and −151 km s−1. A ‘‘Northwest’’ feature, starting northwest of the Western continuum arc, appears faintly at a velocity of +51 km s−1 and then migrates slightly southward until it merges with another feature at a velocity of +78 km s−1. This other feature ‘‘Sweeps’’ in towards Sgr A* as the velocity decreases from +78 to +16 km s−1.