IRDC团块G34 .43+00.24 MM3：DNC/HNC比值的ALMA观测
ALMA Observations of the IRDC Clump G34.43+00.24 MM3: DNC/HNC Ratio
摘要：
我们用阿塔卡马大型毫米/亚毫米阵（ALMA）观测到了与DNC $J$ =3- 2、HN $^{13}$ C $J$ =3- 2和N $_2$ H $^+$ $J$ =3- 2红外暗云有关的团簇G34.43+00.24 MM 3。N $_2$ H $^+$发射在热核和外流附近相对较弱，其分布与CS发射明显反相关。这一结果表明，一个年轻的外流是与冷的环境气体相互作用。HN $^{13}$ C发射是紧凑的，主要从热核发出，而DNC发射是围绕热核扩展的。因此，DNC和HN $^{13}$ C的排放痕迹温暖地区附近的原恒星不同。DNC发射比HN $^{13}$ C发射更强，朝向该团块的大部分。在相位中心周围的$15^{\prime\prime} \times 15^{\prime\prime}$区域内平均的DNC/HNC丰度比高于0.06。该比值远高于先前通过DNC和HN $^{13}$ C $J$ =1--0（$\sim$ 0.003）的单皿观测获得的值。用单碟望远镜观测到的DNC和HNC辐射似乎可以追踪到低密度的包络，而用ALMA观测到的则可以追踪到高密度和高氘化的区域。为了研究致密核中DNC和HNC的行为，我们将观测结果与化学模型结果进行了比较。考虑到这些结果，我们认为，低的DNC/HNC比在高质量源获得的单碟观测至少部分是由于低填充因子的高密度区域。
英文摘要：
We have observed the clump G34.43+00.24 MM3 associated with an infrared dark cloud in DNC $J$=3--2, HN$^{13}$C $J$=3--2, and N$_2$H$^+$ $J$=3--2 with the Atacama Large Millimeter/submillimeter Array (ALMA). The N$_2$H$^+$ emission is found to be relatively weak near the hot core and the outflows, and its distribution is clearly anti-correlated with the CS emission. This result indicates that a young outflow is interacting with cold ambient gas. The HN$^{13}$C emission is compact and mostly emanates from the hot core, whereas the DNC emission is extended around the hot core. Thus, the DNC and HN$^{13}$C emission traces warm regions near the protostar differently. The DNC emission is stronger than the HN$^{13}$C emission toward most parts of this clump. The DNC/HNC abundance ratio averaged within a $15^{\prime\prime} \times 15^{\prime\prime}$ area around the phase center is higher than 0.06. This ratio is much higher than the value obtained by the previous single-dish observations of DNC and HN$^{13}$C $J$=1--0 ($\sim$0.003). It seems likely that the DNC and HNC emission observed with the single-dish telescope traces lower density envelopes, while that observed with ALMA traces higher density and highly deuterated regions. We have compared the observational results with chemical-model results in order to investigate the behavior of DNC and HNC in the dense cores. Taking these results into account, we suggest that the low DNC/HNC ratio in the high-mass sources obtained by the single-dish observations are at least partly due to the low filling factor of the high density regions.
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