NH3 in Orion-KL: A new interpretation

We interpret the observations of ammonia in Orion-KL in a way which greatly simplifies the understanding of single-dish and VLA data. In this new picture, there are only two velocity components: the ''spike'' component from the quiscent molecular cloud and the ''hot core'' component from both streaming and ''stationary'' gas in the 18 km s-1 outflow from the compact infrared source IRc2. What has been interpreted previously as the NH3 ''plateau'' from high-velocity gas is mainly the blended hyperfine satellite emission from the ''hot core'' component. The ammonia lines are highly optically thick (tau>10), and NH3 column densities reach 5 x 1018 cm-2. Kinetic temperatures in the outflow region are about 200 K, and NH3 is probably collisionally excited at hydrogen densities of 108--109 cm-3. Ammonia may be highly overabundant in this dense and warm gas and may tie up a considerable fraction of the available nitrogen. The maps can be interpreted as showing a clumpy, expanding, and turbulent shell advancing into the densest part of the Orion-KL region