发表机构
INAF - Istituto di Radioastronomia di Bologna; Haystack Observatory, Massachusetts Institute of Technology; Instituto de Radioastronomía y Astrofísica (IRyA-UNAM); Department of Astronomy, School of Science, The University of Tokyo; National Astronomical Observatory of Japan, National Institutes of Natural Sciences（意大利国家天体物理研究所射电天文研究所博洛尼成分所; 海斯塔克天文台，麻省理工学院; 无线电天文学与天体物理学研究所（墨西哥国立自治大学）; 东京大学理学部天文学系; 日本国立天文台，自然科学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过ALMA观测发现约15%的大质量团块未碎裂，表明引力而非湍流主导早期碎裂，支持层级式引力驱动模型。
AI 中文摘要
我们对大质量团块早期碎裂阶段的研究揭示了一个显著的反常现象：CoCoA样本中约15%的源完全没有发生碎裂。这些源可能代表了核形成之前的初始条件。我们研究了这些源是否确实处于核形成的起始阶段，以及引力还是湍流主导了它们的早期碎裂。我们通过ALMA对三个跨越这一阶段的大质量团块的观测，研究了从均匀气体到活跃星团形成的转变，并比较了湍流主导和引力主导的团块碎裂模型的对比预测。碎裂的源表现出更高的平均n(H$_2$)密度，其核到包层的密度对比度比最小碎裂的源大5-6倍。所有源都显示出与它们的线宽和引力速度相当的pc尺度速度差异。这表明线宽由大尺度运动主导，而后者由引力驱动。高CH$_3$OH丰度和质量累积时间尺度与天体化学模型一致，在该模型中复杂分子在核出现之前的中间密度下形成。我们分析中的所有独立诊断都与最小碎裂团块处于早期演化阶段一致，可能标志着核碎裂的开始。如果湍流是碎裂的主要驱动因素，那么具有相当马赫数的源应表现出相似的结构特性。相反，我们观察到密度对比度和碎裂程度的显著变化。这些发现挑战了湍流支持的模型，并支持层级式、引力驱动的团块碎裂模型，在该模型中大尺度有序运动占观测线宽的显著比例，并驱动团块向越来越致密和碎裂的状态演化。
英文摘要
Our study of the early stages of fragmentation in massive clumps has revealed a striking anomaly: $\sim15\%$ of the CoCoA sample exhibit no fragmentation at all. These sources could represent the initial conditions before core formation. We investigate whether these sources are indeed at the onset of core formation, and whether gravity or turbulence dominates their early fragmentation. We study the transition from uniform gas to active cluster formation, and compare contrasting predictions of turbulence- and gravity-dominated models of clump fragmentation through ALMA observations of three massive clumps spanning this phase. The fragmented source exhibits higher average $n$(H$_2$) and a core-to-envelope density contrast 5-6 times larger than the minimally fragmented sources. All sources display pc-scale velocity differences comparable to their linewidths and gravitational velocities. This suggests that the linewidth is dominated by the large-scale motions, and that the latter are driven by gravity. The high CH$_3$OH abundances and the mass build-up timescales align with astrochemical models where complex molecules form at intermediate densities before the appearance of cores. All independent diagnostics in our analysis are consistent with the minimally fragmented clumps being an early evolutionary phase, potentially marking the onset of core fragmentation. If turbulence were the primary driver of fragmentation, sources with comparable Mach numbers should exhibit similar structural properties. Instead, we observe significant variations in density contrast and fragmentation. These findings challenge turbulence-supported models and lend support to hierarchical, gravity-driven models of clump fragmentation, where large-scale ordered motions account for a significant fraction of the observed linewidths and drive the evolution of the clump toward increasingly dense and fragmented states.
CommentsA&A, accepted for publication
