Non-LTE Effects in Ammonia

Abstract

The non-LTE effects in the NH3 (J, K) = (1, 1) absorption toward the DR 21 H II region have been investigated using a spatial resolution of 17-3''. 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 NH3 (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 NH3 (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.