EARLIEST STAGES OF PROTOCLUSTER FORMATION: SUBSTRUCTURE AND KINEMATICS OF STARLESS CORES IN ORION
EARLIEST STAGES OF PROTOCLUSTER FORMATION: SUBSTRUCTURE AND KINEMATICS OF STARLESS CORES IN ORION
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DOI：
10.1088/0004-637x/772/2/100
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
Katherine I. Lee;L. Looney;S. Schnee;Zhi-Yun Li
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作者：
Katherine I. Lee;L. Looney;S. Schnee;Zhi-Yun Li
我们使用 IRAM 30 m 望远镜研究猎户座中 9 个 0.1 pc 尺度核心的结构和运动学，并使用 CARMA 以更高分辨率研究其中 8 个核心，使用 CS(2-1) 作为主要示踪剂。无星核心的单碟矩零图显示了中心柱密度范围为 7 至 42 × 1023 cm−2 且 LTE 质量范围为 20 M☉ 至 154 M☉ 的单一结构。然而，在较高的 CARMA 分辨率（5 英寸）下，除了一个碎片之外的所有核心都分成 3-5 个组件。尽管包含磁场可能会减少预测的碎片数量并提高模型一致性，但与某些湍流碎片模型中发现的碎片数量相比，碎片数量较少。这一结果表明，从秒差距尺度的分子云到亚秒差距核心的碎片化继续发生在无星核心内部。无星核心及其碎片嵌入更大的丝状结构中，这可能在核心形成和破碎中发挥了作用。大多数岩心显示出明显的速度梯度，幅度范围为 1.7 至 14.3 km s−1 pc−1。我们对其中一个进行了详细建模，发现其光谱最好的解释是沿着细丝向核心中心汇聚的流动；其他核中的梯度可以类似地建模。我们推断质量流入率为 ∼2 × 10−3 M☉ yr−1，原则上该速率足以克服辐射压力并允许大规模恒星形成。然而，核心包含多个碎片，目前尚不清楚快速流入是否会主要促进单个大质量恒星或一群较低质量天体的生长。我们得出的结论是，沿着细丝的快速超音速会聚流在大质量恒星和星团的形成中发挥着重要作用。
We study the structure and kinematics of nine 0.1 pc scale cores in Orion with the IRAM 30 m telescope and at higher resolution eight of the cores with CARMA, using CS(2–1) as the main tracer. The single-dish moment zero maps of the starless cores show single structures with central column densities ranging from 7 to 42 × 1023 cm−2 and LTE masses from 20 M☉ to 154 M☉. However, at the higher CARMA resolution (5″), all of the cores except one fragment into 3–5 components. The number of fragments is small compared to that found in some turbulent fragmentation models, although inclusion of magnetic fields may reduce the predicted fragment number and improve the model agreement. This result demonstrates that fragmentation from parsec-scale molecular clouds to sub-parsec cores continues to take place inside the starless cores. The starless cores and their fragments are embedded in larger filamentary structures, which likely played a role in the core formation and fragmentation. Most cores show clear velocity gradients, with magnitudes ranging from 1.7 to 14.3 km s−1 pc−1. We modeled one of them in detail, and found that its spectra are best explained by a converging flow along a filament toward the core center; the gradients in other cores may be modeled similarly. We infer a mass inflow rate of ∼2 × 10−3 M☉ yr−1, which is in principle high enough to overcome radiation pressure and allow for massive star formation. However, the core contains multiple fragments, and it is unclear whether the rapid inflow would feed the growth of primarily a single massive star or a cluster of lower mass objects. We conclude that fast, supersonic converging flow along filaments play an important role in massive star and cluster formation.