[论文解读] The molecular gas content of the Pipe Nebula I. Direct evidence of outflow-generated turbulence in B59?

A. Duarte-Cabral, A. Chrysostomou+5 more|ORCA Online Research @Cardiff (Cardiff University)|May 18, 2012

Astrophysics and Star Formation Studies参考文献 49被引用 17

一句话总结

本研究利用詹姆斯克拉克马克斯韦尔望远镜（JCMT）HARP对猎户座分子云B59区域的CO同位素分子进行观测，证明原恒星喷流可直接将湍流注入致密分子气体，使谱线宽度从约0.3 km s⁻¹增加至约1 km s⁻¹，并使激发温度升高2–3 K。结果表明，喷流提供的湍流动能足以在亚秒差距量级上支持团块抵抗坍缩，且喷流能量中不足一半转化为湍流，表明其在安静、低质量核心中调节恒星形成动力学方面具有关键作用。

ABSTRACT

The Pipe Nebula is a molecular cloud hosting the B59 region as its only active star-forming clump. While the particular importance of outflows in active star forming regions is subject of debate, the quiet nature of the gas in B59 makes it a good site to directly see the impact of protostellar feedback on the quiescent dense gas. Using HARP at the JCMT, we mapped the B59 region with the J=3-2 transition of 12CO to study the kinematics and energetics of the outflows, and 13CO and C18O to study the overall dynamics of the ambient cloud, the physical properties of the gas, and the hierarchical structure of the region. The B59 region has a total of 30Msun of cold and quiescent material, mostly gravitationally bound, with narrow line widths throughout. Such low levels of turbulence in non-star-forming sites of B59 are indicative of the intrinsic initial conditions of the cloud. On the other hand, close to the forming protostars the impact of the outflows is observed as a localised increase of both line widths from 0.3 to 1 km/s, and 13CO excitation temperatures by 2-3K. The impact of the outflows is also evident in the low column density material which shows signs of being pushed, shaped and carved by the outflow bow shocks as they pierce their way out of the cloud. Much of this structure is readily apparent in a dendrogram analysis of the cloud. The low mass of B59 together with its intrinsically quiescent gas and small number of protostars, allows the identification of specific regions where the outflows from the embedded sources interact the dense gas. Our study suggests that outflows are an important mechanism for injecting and sustaining supersonic turbulence at sub-parsec size scales. We find that less than half of the outflow energy is deposited as turbulent energy of the gas, however this turbulent energy is sufficient to slow down the collapse of the region.

研究动机与目标

• 研究原恒星喷流对猎户座分子云B59区域动力学及能量收支的影响。
• 确定喷流是否是致密、安静分子气体中湍流的重要来源，特别是在低质量、低速度环境中。
• 评估喷流能量转化为湍流运动的效率及其在支持云团抵抗引力坍缩中的作用。
• 比较B59等安静区域与猎户座Serpens等更活跃区域在喷流驱动湍流可探测性上的差异。
• 评估初始气体条件在决定喷流驱动湍流可观测性及其影响中的作用。

提出的方法

• 利用詹姆斯克拉克马克斯韦尔望远镜（JCMT）上的HARP仪器，对B59区域在12 CO J=3→2、13 CO J=3→2和C 18 O J=3→2跃迁线进行映射观测。
• 通过13 CO和C 18 O的谱线轮廓推导气体温度、柱密度和速度弥散度，识别出湍流增强区域。
• 应用树状图分析法分解团块的分层结构，并结合喷流活动解释其运动学特征。
• 通过估算原恒星源的动能和动量注入量，量化喷流的能量学，并与周围气体中的湍流动能进行比较。
• 通过比较引力势能与湍流动能，评估核心中的动力学支持状态。
• 使用GILDAS和Starlink软件进行数据降噪与分析，特别关注 beam-averaged 谱线宽度和激发温度估计。

实验结果

研究问题

• RQ1 B59中原恒星喷流在致密、安静气体中产生可探测湍流的程度如何？
• RQ2 喷流能量与B59核心中湍流能和引力能相比如何？
• RQ3 为何B59中喷流驱动的湍流比在Serpens等更活跃区域更容易探测？
• RQ4 在低质量、低速度分子核心中，喷流能量转化为湍流运动的效率是多少？
• RQ5 观测到的湍流是否能支持B59团块抵抗引力坍缩？若能，这种支持能持续多久？

主要发现

• B59区域包含约30 M⊙的冷、安静、引力束缚的气体，非恒星形成区的谱线宽度极窄（~0.3 km s⁻¹）。
• 在原恒星附近，C 18 O谱线宽度从~0.3 km s⁻¹增至~1 km s⁻¹，13 CO激发温度升高2–3 K，表明存在局部喷流驱动的湍流。
• 喷流将低柱密度气体塑造成弓形激波状结构，树状图分析可清晰识别，证实其在改变云团形态中的作用。
• 喷流能量中不足一半在喷流附近区域转化为湍流动能，其余能量沉积于核心之外。
• 湍流动能输入足以在亚秒差距尺度（~0.1–0.3 pc）上支持B59团块抵抗坍缩，表现为动能与势能相当。
• 仅当初始气体谱线宽度较低（≤0.4 km s⁻¹）时，喷流驱动的湍流才可被探测到，这解释了为何在Serpens等更湍流的区域中即使谱线宽度相似也难以观测到该现象。