L1688相干堆芯中普遍存在的$\rm NH_3$超声速分量
Ubiquitous $\rm NH_3$ supersonic component in L1688 coherent cores
摘要：
背景：恒星的形成发生在分子云的冷密核心中。早期的观测发现，致密的核心表现出亚音速的非热速度分散。相比之下，CO观测表明，周围的大尺度云是温暖的，并有超音速的速度色散。目的：我们的目标是研究氨（$\rm NH_3$）分子线轮廓与精致的敏感性对相干核心在L1688，以研究其运动学性质前所未有的细节。方法：我们使用绿岸氨调查（GAS）第一次数据发布（DR1）的$\rm NH_3$（1，1）和（2，2）数据。我们首先将数据平滑到更大的1'束，以获得比DR1图更广泛的速度色散和动力学温度图。然后，我们确定了云中的相干核心，并分析了平均线轮廓的核心。结果如下：这是第一次，我们检测到一个微弱的（平均$\rm NH_3$（1，1）峰值亮度$<$ 0.25 K的$T_{MB}$），超声成分对所有的相干核心在L1688。我们拟合了两个组件，一个宽的和一个窄的，并推导出每个组件的动力学温度和速度分散。朝向所有核心的宽分量具有超音速线宽（$\mathcal{M}_S \ge 1$）。与单分量拟合的结果相比，该分量使窄致密堆芯分量的速度离散估计值平均偏差$\approx$ 28%，使动力学温度平均偏差$\approx$ 10%。结论：忽略这种普遍存在的广泛的组件对所有相干核心导致典型的单分量拟合高估的温度和速度色散。这会影响根据$\rm NH_3$观测结果估计的岩心的详细物理结构和稳定性。
英文摘要：
Context : Star formation takes place in cold dense cores in molecular clouds. Earlier observations have found that dense cores exhibit subsonic non-thermal velocity dispersions. In contrast, CO observations show that the ambient large-scale cloud is warmer and has supersonic velocity dispersions. Aims : We aim to study the ammonia ($\rm NH_3$) molecular line profiles with exquisite sensitivity towards the coherent cores in L1688 in order to study their kinematical properties in unprecedented detail. Methods : We used $\rm NH_3$ (1,1) and (2,2) data from the first data release (DR1) in the Green Bank Ammonia Survey (GAS). We first smoothed the data to a larger beam of 1' to obtain substantially more extended maps of velocity dispersion and kinetic temperature, compared to the DR1 maps. We then identified the coherent cores in the cloud and analysed the averaged line profiles towards the cores. Results : For the first time, we detected a faint (mean $\rm NH_3$(1,1) peak brightness $<$0.25 K in $T_{MB}$), supersonic component towards all the coherent cores in L1688. We fitted two components, one broad and one narrow, and derived the kinetic temperature and velocity dispersion of each component. The broad components towards all cores have supersonic linewidths ($\mathcal{M}_S \ge 1$). This component biases the estimate of the narrow dense core component's velocity dispersion by $\approx$28% and the kinetic temperature by $\approx$10%, on average, as compared to the results from single-component fits. Conclusions : Neglecting this ubiquitous presence of a broad component towards all coherent cores causes the typical single-component fit to overestimate the temperature and velocity dispersion. This affects the derived detailed physical structure and stability of the cores estimated from $\rm NH_3$ observations.
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