Global collapse of molecular clouds as a formation mechanism for the most massive stars
Global collapse of molecular clouds as a formation mechanism for the most massive stars
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DOI：
10.1051/0004-6361/201321318
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发表时间：
2013-07
影响因子：
6.5
通讯作者：
N. Peretto;G. Fuller;A. Duarte-Cabral;A. Avison;P. Hennebelle;J. Pineda;P. Andre';S. Bontemps;F. Motte;N. Schneider;S. Molinari
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文献类型：
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作者：
N. Peretto;G. Fuller;A. Duarte-Cabral;A. Avison;P. Hennebelle;J. Pineda;P. Andre';S. Bontemps;F. Motte;N. Schneider;S. Molinari
原始分子云碎裂与大规模吸积的相对重要性仍有待在大质量核心/星星形成的背景下进行评估。研究围绕恒星祖先的致密气体的运动学可以告诉我们大规模物质流动对恒星形成核心质量增长的影响程度。在这里，我们提出了一个全面的数据集的5500（±800）M的红外暗云SDC335.579-0.272（以下简称SDC 335），它表现出一个网络的冷，密集，秒差距长的细丝。阿塔卡马大型毫米波阵列（阿尔马）第0周期的观测揭示了两个巨大的恒星形成核心，MM 1和MM 2，位于SDC 335的中心，在那里细丝相交。在0.05秒差距的源直径内，气体质量为545（-385+770）M，MM 1是银河系中观测到的最大质量、最致密的原恒星核心之一。整体而言，SDC 335可能会形成一个类似猎户座梯形星团的OB星团。阿尔马和Mopra对SDC 335稠密气体的单碟观测进一步表明，这个中心-暗条系统的运动学与云的全球坍缩一致。这些分子线数据表明，落入速度Vinf = 0.7（± 0.2）km s-1，总质量落入率Δ Inf = 2.5（±1.0）× 10-3 M·yr-1，朝向SDC 335的中心pc大小区域。这个下沉速率在每一个自由落体时间（tff = 3 × 105年）内将750（±300）M的气体带到云的中心。这足以使已经存在于pc大小的中心区域的质量增加一倍，在3.5-1.0+2.2 × tff内。这些数值表明，在过去的百万年里，SDC 335的全球性坍缩导致了早期O型星星祖先在云的引力势阱中心的形成。
The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to be assessed in the context of massive core/star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-forming cores. Here we present a comprehensive dataset of the 5500(±800) M⊙ infrared dark cloud SDC335.579-0.272 (hereafter SDC335), which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array (ALMA) Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where the filaments intersect. With a gas mass of 545(-385+770) M⊙ contained within a source diameter of 0.05 pc, MM1 is one of the most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially form an OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335 dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapse of the cloud. These molecular-line data point towards an infall velocity Vinf = 0.7( ± 0.2) km s-1, and a total mass infall rate Ṁinf ≃ 2.5(±1.0) × 10-3 M⊙ yr-1 towards the central pc-size region of SDC335. This infall rate brings 750(±300) M⊙ of gas to the centre of the cloud per free-fall time (tff = 3 × 105 yr). This is enough to double the mass already present in the central pc-size region in 3.5-1.0+2.2 × tff. These values suggest that the global collapse of SDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of the cloud’s gravitational potential well.