海马吞下了什么？海马红外暗云化学条件的APEX 170 GHz观测
What did the seahorse swallow? APEX 170 GHz observations of the chemical conditions in the Seahorse infrared dark cloud
摘要：
我们使用APEX望远镜观测了在大约170 GHz频率下发生的谱线，这些谱线朝向沿着海洋海马红外暗云的全部范围的14个位置。共检测到6条谱线跃迁（$\geq3σ$），即SO $(N_J=4_4-3_3)$、H $^{13}$ CN $(J=2-1)$、H $^{13}$ CO $^+(J=2-1)$、SiO $(J=4-3)$、HN $^{13}$ C $(J=2-1)$和C $_2$ H $(N=2-1)$。SO、H $^{13}$ CO、$^+$和HN $^{13}$ C在各来源中均有检出，C、$_2$ H和H $^{13}$ CN的检出率分别为92.9%和85.7%。只有一个源（SMM 3）显示出可检测的SiO排放（7.1%的检测率）。3个团块（SMM 5、6和7）显示SO、H $^{13}$ CN、H $^{13}$ CO $^+$、HN $^{13}$ C和C $_2$ H吸收线。我们发现三个衍生分子丰度之间的正相关性，其中C $_2$ H和HN $^{13}$ C和HN $^{13}$ C和H $^{13}$ CO $^+$之间的相关性最显著（相关系数$r\simeq0.9$）。统计上最显着的演变趋势，我们发现的下降，在C $_2$ H丰度和$[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$的比例，作为集群从一个红外暗阶段演变到一个红外亮阶段，然后到一个HII区域。我们发现不同分子丰度之间的相关性可以理解为来自气相电子（电离度）和原子碳丰度。我们发现的[C $_2$ H]演化指标与以前的研究一致，并可以解释为当团簇温度升高时，特别是在团簇中的热分子核心点燃后，C $_2$ H转化为其他物种（例如CO）。$[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$随团簇演化的降低也可能反映团簇温度的升高，这导致HCN及其$^{13}$ C同位素体的形成增强。
英文摘要：
We used the APEX telescope to observe spectral lines occurring at about 170 GHz frequency towards 14 positions along the full extent of the filamentary Seahorse infrared dark cloud. Six spectral line transitions were detected ($\geq3σ$) altogether, namely, SO$(N_J=4_4-3_3)$, H$^{13}$CN$(J=2-1)$, H$^{13}$CO$^+(J=2-1)$, SiO$(J=4-3)$, HN$^{13}$C$(J=2-1)$, and C$_2$H$(N=2-1)$. While SO, H$^{13}$CO$^+$, and HN$^{13}$C were detected in every source, the detection rates for C$_2$H and H$^{13}$CN were 92.9% and 85.7%, respectively. Only one source (SMM 3) showed detectable SiO emission (7.1% detection rate). Three clumps (SMM 5, 6, and 7) showed the SO, H$^{13}$CN, H$^{13}$CO$^+$, HN$^{13}$C, and C$_2$H lines in absorption. We found three positive correlations among the derived molecular abundances, of which those between C$_2$H and HN$^{13}$C and HN$^{13}$C and H$^{13}$CO$^+$ are the most significant (correlation coefficient $r\simeq0.9$). The statistically most significant evolutionary trends we uncovered are the drops in the C$_2$H abundance and in the $[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$ ratio as the clump evolves from an IR dark stage to an IR bright stage and then to an HII region. The correlations we found between the different molecular abundances can be understood as arising from the gas-phase electron (ionisation degree) and atomic carbon abundances. The [C$_2$H] evolutionary indicator we found is in agreement with previous studies, and can be explained by the conversion of C$_2$H to other species (e.g. CO) when the clump temperature rises, especially after the ignition of a hot molecular core in the clump. The decrease of $[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$ as the clump evolves is also likely to reflect the increase in the clump temperature, which leads to an enhanced formation of HCN and its $^{13}$C isotopologue.
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