Non-LTE Effects in Ammonia

The non-LTE effects in the NH 3 ( J , K ) = (1, 1) absorption toward the DR 21 H II region have been investigated using a spatial resolution of 1 7-3''. The anomalies, found in the satellite hyperfine (HF) components, indicate significant, widespread departures from LTE. We present images of the LTE departure for the inner and outer pairs of NH 3 (1, 1) HF components toward the H II region and find, surprisingly, that the degree of LTE departure for these HF components is spatially anticorrelated . Previous models predicted a spatial correlation. This unexpected result may be explained by a dynamic model involving both the infall and outflow of molecular material. Although weak emission in the redshifted outer HF component is widespread toward the continuum, an unresolved, high brightness temperature (≥600 K) maser is found just southwest of the continuum peak. This is the first proven instance of an interstellar maser in the NH 3 (1, 1) level. The flux density of the maser is larger than the absolute value of the flux density of any of the other HF components (seen in absorption), including the main component.