Kinematics, Kinetic Temperatures, and Column Densities of NH₃in the Orion Hot Core

Abstract

Using the VLA, we have mapped the Orion Hot Core region (full extent 10'') with an angular resolution of ~1'' in the (J,K) = (4,4) and (10, 9) inversion transitions of 14NH3 and an angular resolution of 4'' in the (J,K) = (2,2) and (3, 3) inversion transitions of 15NH3. All of the single-dish flux density for the (10, 9) transition was recovered by the VLA, but a substantial fraction of the flux density in the (4, 4) and 15NH3 (3, 3) lines was not detected. The missing flux density is from the spatially extended "spike" component. Assuming that local thermodynamic equilibrium (LTE) holds, we have calculated the optical depths of the (4, 4) inversion transition for all positions where the main and satellite lines were detected with sufficient signal-to-noise ratio. We combined our (10, 9) data with these (4, 4) line results to produce images of the rotational temperature, Trot, and the column density of ammonia, N(NH3). For the H2 densities in the Hot Core, Trot = Tkin, the kinetic temperature. An additional determination of Tkin and N(NH3) was made by combining our (10, 9) inversion line data with our 15NH3 (3, 3) inversion line results. The 15NH3 inversion transitions have no quadrupole hyperfine structure so that the line shapes are simpler. The moment distribution of the 15NH3 (3, 3) line shows that the largest intensity-weighted line width arises close to the center of the Hot Core region. Thus, we may have discovered a low-luminosity outflow source embedded in the Hot Core. Alternatively, this may be a result of gas motions related to source "I," which is about half a beamwidth from this feature.