NH3(1,1) hyperfine intensity anomalies in the Orion A molecular cloud
NH3(1,1) hyperfine intensity anomalies in the Orion A molecular cloud
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Orion A 分子云中的 NH3 (1,1) 超精细强度异常
DOI：
10.1051/0004-6361/201936661
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发表时间：
2020
影响因子：
6.5
通讯作者：
Zheng Xing-wu
中科院分区：
文献类型：
--
作者：
Zhou Dong-dong;Wu Gang;Esimbek Jarken;Henkel Christian;Zhou Jianjun;Li Da-lei;Ji Wei-guang;Zheng Xing-wu
氨 (NH3) 反演线具有众多超精细成分，是分子云 (MC) 研究中常用的示踪剂。在局部热力学平衡中，NH3(J,K) = (1,1) 跃迁的两条内部卫星线 (ISL) 和两条外部卫星线 (OSL) 预计具有相同的强度。然而，超精细强度异常（HIA）被观察到在恒星形成区域中无处不在，这一特征尚未完全了解。在解决这个问题时，我们发现通过峰强度比计算HIA的方法可能存在缺陷，特别是在处理低速色散光谱时。因此，我们通过 ISL (HIAIS) 和 OSL (HIAOS) 的红移与蓝移积分强度之比定义了 ISL (HIAIS) 和 OSL (HIAOS) 的积分 HIA（统一意味着没有异常），并开发了计算它们的程序。基于此程序，我们对猎户座 A MC 北部的综合 HIA 进行了系统研究。我们发现集成的 HIAIS 和 HIAOS 普遍存在于 Orion A MC 中，并且在 MC 的不同位置没有发现明显的区别。综合HIAIS和HIAOS的中位数分别为0.921±0.003和1.422±0.009，与HIA核心模型一致，与塌陷或膨胀（CE）模型不一致。在这 170 个位置的选择中，两个集成的 HIA 与统一偏差超过 3σ，大多数（166 个）的特征是 HIAIS < 1 和 HIAOS > 1，这表明 HIA 核心模型比 CE 模型发挥着更重要的作用。其余四个位置与CE模型一致。我们将积分 HIA 与对 NH3 柱密度 (N(para-NH3))、动力学温度 (TK)、总速度色散 (σv)、非热速度色散 (σNT) 以及 NH3(J,K) = (1,1) 线 (τ0) 的总不透明度进行比较。综合的HIAIS和HIAOS几乎独立于N(对NH3)。随着 TK、σv 和 σNT 的增加，积分 HIAIS 从 1（无异常）略微下降至约 0.7。积分 HIAOS 与 TK 无关，并且随着 σv 和 σNT 的增加而达到接近 1 的值。积分 HIAIS 几乎与 τ0 无关，而积分 HIAOS 随 τ0 上升，因此表现出更高的异常。 HIA 核心或 CE 模型都无法完全解释这些相关性。
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 (HIAIS) and OSLs (HIAOS) 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 HIAISand HIAOSare commonly present in the Orion A MC and no clear distinction is found at different locations of the MC. The medians of the integrated HIAISand HIAOSare 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 3σfrom unity, most (166) are characterized by HIAIS< 1 and HIAOS> 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-NH3column density (N(para-NH3)), kinetic temperature (TK), total velocity dispersion (σv), non-thermal velocity dispersion (σNT), and the total opacity of the NH3(J,K) = (1,1) line (τ0). The integrated HIAISand HIAOSare almost independent ofN(para-NH3). The integrated HIAISdecreases slightly from unity (no anomaly) to about 0.7 with increasingTK,σv, andσNT. The integrated HIAOSis independent ofTKand reaches values close to unity with increasingσvandσNT. The integrated HIAISis almost independent ofτ0, while the integrated HIAOSrises withτ0, thus showing higher anomalies. These correlations cannot be fully explained by either the HIA core nor the CE model.