扩散分子云中的含硫分子：来自SOFIA/GREAT和IRAM 30米望远镜的新结果
Sulphur-bearing molecules in diffuse molecular clouds: new results from SOFIA/GREAT and the IRAM 30 m telescope
摘要：
我们已经观察到五个含硫分子在前景弥漫分子云躺在视线到五个明亮的连续光源。我们利用SOFIA上的GREAT仪器观测了SH的1383 GHz $^2Π_{3/2} J=5/2-3/2$向恒星形成区W31 C、G29.96-0.02、G34.3+0.1、W 49 N和W51的跃迁，探测到了这五个源的前景吸收; Pico Veleta的IRAM 30 m望远镜上的EMIR接收器检测H $_2$ S 1（10）-1（01），CS J=2-1和SO 3（2）-2（1）跃迁。在朝向这些来源检测到的九种前景吸收组分中，四种检测到的分子的推断柱密度显示出相对恒定的比率，其中N（SH）/N（H $_2$ S）在1.1 - 3.0的范围内，N（CS）/N（H $_2$ S）在0.32 - 0.61的范围内，并且N（SO）/N（H $_2$ S）在0.08 - 0.30的范围内。所观察到的SH/H $_2$比--在（0.5-2.6）$\times 10^{-8}$范围内--表明SH（和其它含硫分子）占气相硫核的<< 1%。然而，所观察到的含硫分子的丰度大大超过了冷扩散分子云的标准模型的预测，为提高吸热反应速率的温度升高或离子中性漂移提供了进一步的证据。我们考虑了激波和湍流耗散区（TDR）模型中观测到的丰度比。使用TDR模型，我们发现，在大尺度的扩散ISM湍流能量是足够的解释所观察到的柱密度的SH和CS。然而，标准的激波和TDR模型不能再现H $_2$ S和SO的柱密度，误差约为10倍;更精细的激波模型--其中考虑了H $_3$ S $^+$的解离重组产生的SH分子相对于H $_2$的速度漂移--将这种差异减小到约3倍。
英文摘要：
We have observed five sulphur-bearing molecules in foreground diffuse molecular clouds lying along the sight-lines to five bright continuum sources. We have used the GREAT instrument on SOFIA to observe the 1383 GHz $^2Π_{3/2} J=5/2-3/2$ transitions of SH towards the star-forming regions W31C, G29.96-0.02, G34.3+0.1, W49N and W51, detecting foreground absorption towards all five sources; and the EMIR receivers on the IRAM 30m telescope at Pico Veleta to detect the H$_2$S 1(10)-1(01), CS J=2-1 and SO 3(2)-2(1) transitions. In nine foreground absorption components detected towards these sources, the inferred column densities of the four detected molecules showed relatively constant ratios, with N(SH)/N(H$_2$S) in the range 1.1 - 3.0, N(CS)/N(H$_2$S) in the range 0.32 - 0.61, and N(SO)/N(H$_2$S) in the range 0.08 - 0.30. The observed SH/H$_2$ ratios - in the range (0.5-2.6) $\times 10^{-8}$ - indicate that SH (and other sulphur-bearing molecules) account for << 1% of the gas-phase sulphur nuclei. The observed abundances of sulphur-bearing molecules, however, greatly exceed those predicted by standard models of cold diffuse molecular clouds, providing further evidence for the enhancement of endothermic reaction rates by elevated temperatures or ion-neutral drift. We have considered the observed abundance ratios in the context of shock and turbulent dissipation region (TDR) models. Using the TDR model, we find that the turbulent energy available at large scale in the diffuse ISM is sufficient to explain the observed column densities of SH and CS. Standard shock and TDR models, however, fail to reproduce the column densities of H$_2$S and SO by a factor of about 10; more elaborate shock models - in which account is taken of the velocity drift, relative to H$_2$, of SH molecules produced by the dissociative recombination of H$_3$S$^+$ - reduce this discrepancy to a factor ~ 3.
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