ALMA Observations of Fragmentation, Substructure, and Protostars in High-mass Starless Clump Candidates
ALMA Observations of Fragmentation, Substructure, and Protostars in High-mass Starless Clump Candidates
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DOI：
10.3847/1538-4357/ab40ca
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发表时间：
2019-08
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通讯作者：
B. Svoboda;Y. Shirley;A. Traficante;C. Battersby;G. Fuller;Qizhou Zhang;H. Beuther;N. Peretto;C. Brogan;T. Hunter
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作者：
B. Svoboda;Y. Shirley;A. Traficante;C. Battersby;G. Fuller;Qizhou Zhang;H. Beuther;N. Peretto;C. Brogan;T. Hunter
高质量恒星和原星团的初始物理条件仍然很难确定。为此，我们提出了第一个有针对性的阿尔马波段6 1.3毫米连续谱和光谱线调查对高质量的无星团块候选人，选择一个样本的12个最大的候选人（）内。联合阵列图具有高空间分辨率（，θsyn <$0.″8）和高点源质量完整性（或列密度灵敏度）。我们发现了以前未被发现的低光度星星形成的路标和双极外流和其他签名对11出12块，表明目前的MIR/FIR银河平面调查是不完整的低和中等质量的原恒星（），并强调高分辨率的后续行动的必要性。我们比较了一个子集的观测核心与一套辐射传输模型的无星核心。我们发现了一个高质量的无星核心候选者与模型推导的质量一致时，集成的大小尺度。未分辨的核心与外部加热的普卢默密度分布的辐射传输模型的拟合度很差，这支持了即使没有检测到外流，它们也是原恒星的解释。在12个团块中，有10个团块观察到具有丰富亚结构的高度碎裂。我们从地图中提取源，使用树状图来研究特征碎片长度尺度。最近邻分离，当用蒙特卡罗随机抽样对投影进行校正时，与等于块平均热牛仔裤长度（即，分离等于）。在以前的观察中，在更大的尺度上，看到与湍流牛仔长度或圆柱形热牛仔尺度（）一致的分离，我们的研究结果支持分层碎裂过程，其中最高密度区域不强烈支持湍流或磁场对热引力碎裂的影响。
The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end, we present the first targeted ALMA Band 6 1.3 mm continuum and spectral line survey toward high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates ( ) within . The joint array maps have a high spatial resolution of ( , θsyn ≈ 0.″8) and have high point-source mass-completeness down to at (or column density sensitivity of ). We discover previously undetected signposts of low-luminosity star formation from and bipolar outflows and other signatures toward 11 out of 12 clumps, showing that current MIR/FIR Galactic plane surveys are incomplete to low- and intermediate-mass protostars ( ), and emphasizing the necessity of high-resolution follow-up. We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with when integrated over size scales of . Unresolved cores are poorly fit by radiative transfer models of externally heated Plummer density profiles, supporting the interpretation that they are protostellar even without detection of outflows. A high degree of fragmentation with rich substructure is observed toward 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations, when corrected for projection with Monte Carlo random sampling, are consistent with being equal to the clump average thermal Jeans length ( ; i.e., separations equal to ). In the context of previous observations that, on larger scales, see separations consistent with the turbulent Jeans length or the cylindrical thermal Jeans scale ( ), our findings support a hierarchical fragmentation process, where the highest-density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields.