大质量恒星形成最早阶段的物理条件：红外暗云中氨和CCS的单碟和干涉观测
Physical Conditions of the Earliest Phases of Massive Star Formation: Single-Dish and Interferometric Observations of Ammonia and CCS in Infrared Dark Clouds
摘要：
红外暗云（IRDC）是大质量恒星形成的最早阶段，许多红外暗云中的致密核心，通过毫米连续谱或高临界密度线中的分子发射来追踪，承载着大质量年轻恒星（YSO）。我们使用了罗伯特C。伯德格林班克望远镜（GBT）和卡尔G。Jansky甚大阵列（VLA）绘制了9个IRDC中的NH $_{3}$和CCS，以揭示温度、密度和速度结构，并探索致密（$>10^{22}$ cm $^{-2}$）气体中的化学演化。氨是这些寒冷、密集环境的一种极好的分子示踪剂。IRDC的内部结构和运动学包括速度梯度、细丝和可能的碰撞团块，它们阐明了这些结构及其YSO的形成过程。我们发现了各种各样的子结构，包括不同速度的细丝和小球，有时在正在进行的恒星形成的地点重叠。看来这些IRDC仍然是由分子气体团组装而成的，即使恒星形成已经开始，其中至少有三个似乎与文献中讨论的“枢纽-细丝结构”的形态一致。此外，我们发现这些团块通常在引力能和动能之间接近均分，因此这些结构可能会在多个自由落体时间内幸存下来。关键词：分子数据-- ISM：云--（ISM：）尘埃，灭绝-- ISM：分子--恒星：形成--射电线：ISM
英文摘要：
Infrared Dark Clouds (IRDCs) harbor the earliest phases of massive star formation, and many of the compact cores in IRDCs, traced by millimeter continuum or by molecular emission in high critical density lines, host massive young stellar objects (YSOs). We used the Robert C. Byrd Green Bank Telescope (GBT) and the Karl G. Jansky Very Large Array (VLA) to map NH$_{3}$ and CCS in nine IRDCs to reveal the temperature, density, and velocity structures and explore chemical evolution in the dense ($>10^{22}$ cm$^{-2}$) gas. Ammonia is an excellent molecular tracer for these cold, dense environments. The internal structure and kinematics of the IRDCs include velocity gradients, filaments, and possibly colliding clumps that elucidate the formation process of these structures and their YSOs. We find a wide variety of substructure including filaments and globules at distinct velocities, sometimes overlapping at sites of ongoing star formation. It appears that these IRDCs are still being assembled from molecular gas clumps even as star formation has already begun, and at least three of them appear consistent with the morphology of ``hub-filament structures'' discussed in the literature. Furthermore, we find that these clumps are typically near equipartition between gravitational and kinetic energies, so these structures may survive for multiple free-fall times.Keywords: molecular data -- ISM: clouds -- (ISM:) dust, extinction -- ISM: molecules -- Stars: formation -- radio lines: ISM
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