Abstract
Ammonia (NH3) inversion lines, with their numerous hyperfine components, are a common tracer used in studies of molecular clouds (MCs). In local thermodynamical equilibrium, the two inner satellite lines (ISLs) and the two outer satellite lines (OSLs) of the NH3(J, K) = (1,1) transition are each predicted to have equal intensities. However, hyperfine intensity anomalies (HIAs) are observed to be omnipresent in star formation regions, a characteristic which is still not fully understood. In addressing this issue, we find that the computation method of the HIA by the ratio of the peak intensities may have defects, especially when used to process the spectra with low-velocity dispersions. Therefore, we defined the integrated HIAs of the ISLs (HIA(IS)) and OSLs (HIA(OS)) by the ratio of their redshifted to blueshifted integrated intensities (unity implies no anomaly) and developed a procedure to calculate them. Based on this procedure, we present a systematic study of the integrated HIAs in the northern part of the Orion A MC. We find that integrated HIA(IS) and HIA(OS) are commonly present in the Orion A MC and no clear distinction is found at different locations of the MC. The medians of the integrated HIA(IS) and HIA(OS) are 0.921 +/- 0.003 and 1.422 +/- 0.009, respectively, which is consistent with the HIA core model and inconsistent with the collapse or expansion (CE) model. In the selection of those 170 positions, where both integrated HIAs deviate by more than 3 sigma from unity, most (166) are characterized by HIA(IS) < 1 and HIA(OS) > 1, which suggests that the HIA core model plays a more significant role than the CE model. The remaining four positions are consistent with the CE model. We compare the integrated HIAs with the para-NH3 column density (N(para-NH3)), kinetic temperature (T-K), total velocity dispersion (sigma (v)), non-thermal velocity dispersion (sigma (NT)), and the total opacity of the NH3(J, K) = (1,1) line (tau (0)). The integrated HIA(IS) and HIA(OS) are almost independent of N(para-NH3). The integrated HIA(IS) decreases slightly from unity (no anomaly) to about 0.7 with increasing T-K, sigma (v), and sigma (NT). The integrated HIA(OS) is independent of T-K and reaches values close to unity with increasing sigma (v) and sigma (NT). The integrated HIA(IS) is almost independent of tau (0), while the integrated HIA(OS) rises with tau (0), thus showing higher anomalies. These correlations cannot be fully explained by either the HIA core nor the CE model.