Molecular tracers of the central 12 parsecs of the Galactic center

We have used the BIMA array to image the Galactic center with a 19 pointing mosaic in HCN(1-0), HCO+ (1-0), and H 42 alpha emission with 5 km s(-1) velocity resolution and 13 x 4 angular resolution. The 5' field includes the circumnuclear ring (CND) and parts of the 20 and 50 km s(-1) clouds. HCN(1-0) and HCO+ trace the CND and nearby giant molecular clouds, while the H 42 alpha emission traces the ionized gas in Sgr A West. We find that the CND has a definite outer edge in HCN and HCO+ emission at similar to 45 radius and appears to be composed of two or three distinct streams of molecular gas rotating around the nucleus. Outside the CND, HCN and HCO+ trace dense clumps of high-velocity gas in addition to optically thick emission from the 20 and 50 km s(-1) clouds. A molecular ridge of compressed gas and dust, traced in NH3 emission and self-absorbed HCN and HCO+, wraps around the eastern edge of Sgr A East. Just inside this ridge are several arcs of gas that have been accelerated by the impact of Sgr A East with the 50 km s(-1) cloud. HCN and HCO+ emission trace the extension of the northern arm of Sgr A West, which appears to be an independent stream of neutral and ionized gas and dust originating outside the CND. Broad line widths and OH maser emission mark the intersection of the northern arm and the CND. Comparison to previous NH3 and 1.2 mm dust observations shows that HCN and HCO+ preferentially trace the CND and are weaker tracers of the GMCs than NH3 and dust. We discuss possible scenarios for the emission mechanisms and environment at the Galactic center that could explain the differences in these images.