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arXiv 1206.2115astro-ph.GA
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金牛座分子云中的13 CO核

13CO Cores in Taurus Molecular Cloud

Lei Qian, Di Li, Paul Goldsmith

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46 pages, 23 figures, accepted by ApJ
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摘要：

年轻的恒星在分子核心中形成，分子核心是分子云内的致密凝聚。我们在金牛座分子云中寻找了由$^{13}$ CO $J=1\to 0$辐射示踪的分子核，并研究了它们的性质。我们的数据集具有约1000的空间动态范围（线性图大小与像素大小的比率）和光谱分辨速度信息，它们一起允许系统地检查$^{13}$ CO核在大的连续区域中的分布和动态状态。我们使用经验拟合的CO和CO $_2$冰，以纠正气相CO的耗尽。$^{13}$ CO核心质量函数（$^{13}$ CO CMF）可以更好地拟合对数正态函数比幂律函数。我们还提取核心和计算$^{13}$ CO CMF的基础上的积分强度的$^{13}$ CO和CMF从2 MASS。我们证明了存在核心融合，即速度不相干但柱密度连续的组合结构。核心速度色散（CVD）是核心速度差$δv$的方差，表现出幂律行为，作为表观分离$L$：\ CVD（km/s）$\propto L ({\rm pc})^{0.7}$的函数。这类似于气体速度弥散的拉森定律。$^{13}$ CO芯的峰值速度不偏离环境$^{12}$ CO气体的质心速度超过线宽的一半。核心之间的低速分散，CVD和拉森定律之间的密切相似性，以及核心质心速度和周围气体之间的小分离都表明分子核心从扩散气体中凝结出来，而没有来自恒星形成的额外能量或会聚流的显著影响。

英文摘要：

Young stars form in molecular cores, which are dense condensations within molecular clouds. We have searched for molecular cores traced by $^{13}$CO $J=1\to 0$ emission in the Taurus molecular cloud and studied their properties. Our data set has a spatial dynamic range (the ratio of linear map size to the pixel size) of about 1000 and spectrally resolved velocity information, which together allow a systematic examination of the distribution and dynamic state of $^{13}$CO cores in a large contiguous region. We use empirical fit to the CO and CO$_2$ ice to correct for depletion of gas-phase CO. The $^{13}$CO core mass function ($^{13}$CO CMF) can be fitted better with a log-normal function than with a power law function. We also extract cores and calculate the $^{13}$CO CMF based on the integrated intensity of $^{13}$CO and the CMF from 2MASS. We demonstrate that there exists core blending, i.e.\ combined structures that are incoherent in velocity but continuous in column density. The core velocity dispersion (CVD), which is the variance of the core velocity difference $δv$, exhibits a power-law behavior as a function of the apparent separation $L$:\ CVD (km/s) $\propto L ({\rm pc})^{0.7}$. This is similar to Larson's law for the velocity dispersion of the gas. The peak velocities of $^{13}$CO cores do not deviate from the centroid velocities of the ambient $^{12}$CO gas by more than half of the line width. The low velocity dispersion among cores, the close similarity between CVD and Larson's law, and the small separation between core centroid velocities and the ambient gas all suggest that molecular cores condense out of the diffuse gas without additional energy from star formation or significant impact from converging flows.

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