Origin of the PN molecule in star-forming regions: the enlarged sample
Origin of the PN molecule in star-forming regions: the enlarged sample
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DOI：
10.1093/mnras/stz2446
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发表时间：
2019-11-01
影响因子：
4.8
通讯作者：
Caselli, P.
中科院分区：
文献类型：
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作者：
Fontani, F.;Rivilla, V. M.;Caselli, P.
氮化磷（PN）是在恒星形成区域中检测到数量最多的含磷物种。对该分子的多线研究表明，PN 的激发温度通常低于气体动力学温度，这表明 PN 很可能处于亚热激发条件下。我们提出了一种 PN 分析，其中考虑了 24 个大质量恒星形成区域样本中可能的亚热激发条件。我们用IRAM-30m和APEX望远镜观测了PN（2-1）、（3-2）、（4-3）和（6-5），并在其中15个望远镜中检测到了PN线。加上之前工作中在 PN 中检测到的 9 个类似源，我们分析了迄今为止最大的恒星形成区域样本，该样本由 33 个源组成，总共检测到 24 次（其中 13 次是新检测到的）。因此，我们将 PN 中检测到的恒星形成区域的数量增加了 2 倍以上。我们的分析表明，PN 线确实是亚热激发的，但可以通过单一激发温度很好地描述。我们比较了 PN 和 SiO（一种典型的激波示踪剂）的谱线轮廓和分数丰度，发现几乎所有在 PN 中检测到的物体都具有高速 SiO 翼。此外，SiO和PN丰度相对于H-2在几个数量级上相关，并且与气体温度不相关。这清楚地表明PN的产生与冲击气体的存在密切相关，并排除了基于冰粒地幔热蒸发的替代方案。
Phosphorus nitride (PN) is the P-bearing species with the highest number of detections in star-forming regions. Multiline studies of the molecule have shown that the excitation temperature of PN is usually lower than the gas kinetic temperature, suggesting that PN is likely in conditions of sub-thermal excitation. We present an analysis of PN that takes the possible sub-thermal excitation conditions into account in a sample of 24 massive star-forming regions. We observed PN (2-1), (3-2), (4-3), and (6-5) with the IRAM-30m and APEX telescopes and detected PN lines in 15 of them. Together with 9 similar sources detected in PN in previous works, we have analysed the largest sample of star-forming regions to date, made of 33 sources with 24 detections in total (among which 13 are new detections). Hence, we have increased the number of star-forming regions detected in PN by more than a factor 2. Our analysis indicates that the PN lines are indeed sub-thermally excited, but well described by a single excitation temperature. We have compared line profiles and fractional abundances of PN and SiO, a typical shock tracer, and found that almost all objects detected in PN have high-velocity SiO wings. Moreover, the SiO and PN abundances with respect to H-2 are correlated over several orders of magnitude, and uncorrelated with gas temperature. This clearly shows that the production of PN is strongly linked to the presence of shocked gas, and rules out alternative scenarios based on thermal evaporation from iced grain mantles.