Discovery of a Dusty Ring in the Coalsack: A Dense Core Caught in the Act of Formation?
Discovery of a Dusty Ring in the Coalsack: A Dense Core Caught in the Act of Formation?
复制标题
在煤袋中发现尘土飞扬的环：形成过程中捕获的致密核心？
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
J. Alves
中科院分区：
文献类型：
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作者：
C. Lada;T. Huard;L. J. Crews;J. Alves
我们提出了一个新的红外消光研究球体2，最不透明的分子云核在科尔萨克复合体。利用ESO新技术望远镜获得的深度近红外成像观测，我们能够比以前更详细地检查球体的结构。我们发现这个球体最突出的结构特征是一个强大的尘埃柱密度中心环，这在对这片云的较低分辨率的研究中并不明显。这个环代表了一个高密度和高压力的区域，很可能是一个瞬变结构。对于球状云几何结构，环对应于一个致密的高压内壳，它不可能与周围环境处于动态平衡，因为在云层的中心区域似乎没有压力源来支持壳体免受重力并防止其向内内爆。环向内崩塌的时间尺度不到2×105年，这表明该球体处于极早期的演化阶段，可能正处于形成中心凝聚致密核或BOK球体的过程中。在其中心区域之外，球体呈现出一种良好的密度分布，其形状非常类似于稳定的Bonnor-Ebert球体。利用瑞典的ESO亚毫米望远镜，我们还获得了接近云层中心的C18O光谱。CO观测表明，该球体是一个受引力约束的天体。对CO谱线轮廓的分析表明，很可能是由湍流引起的显著的非热气体运动。作为一个整体，球体可能正在演化到准静态动态平衡的全球状态，在这种状态下，热压和湍流压力平衡重力。
We present a new infrared extinction study of Globule 2, the most opaque molecular cloud core in the Coalsack complex. Using deep near-infrared imaging observations obtained with the ESO New Technology Telescope, we are able to examine the structure of the globule in significantly greater detail than previously possible. We find the most prominent structural feature of this globule to be a strong central ring of dust column density that was not evident in lower resolution studies of this cloud. This ring represents a region of high density and pressure that is likely a transient structure. For a spherical cloud geometry, the ring would correspond to a dense inner shell of high pressure that could not be in dynamical equilibrium with its surroundings, since there appear to be no sources of pressure in the central regions of the cloud that could support the shell against gravity and prevent its inward implosion. The timescale for the inward collapse of the ring would be less than 2 × 105 yr, suggesting that this globule is in an extremely early stage of evolution, and is perhaps being caught in the process of forming a centrally condensed dense core or Bok globule. Outside its central regions, the globule displays a well-behaved density profile whose shape is very similar to that of a stable Bonnor-Ebert sphere. Using the Swedish ESO Submillimeter Telescope, we also obtained a C18O spectrum toward the center of the cloud. The CO observation indicates that the globule is a gravitationally bound object. Analysis of the CO line profile reveals significant nonthermal gas motions likely due to turbulence. As a whole, the globule may be evolving to a global state of quasi-static dynamical equilibrium in which thermal and turbulent pressure balance gravity.