Taurus分子云中的密度方差马赫数关系
The Density Variance Mach Number Relation in the Taurus Molecular Cloud
摘要：
分子云中的超音速湍流是产生密度增强的关键因素，密度增强可能随后继续形成恒星。湍流越强--马赫数越高--密度波动预计越极端。数值模型预测密度方差随均方根马赫数的增加而增加，其形式为：σ ^{2}_{rho/ rho_{0} } = b^{2}M^{2}，其中b是一个数值估计的参数，这种预测形成了大量恒星形成分析模型的基础。我们提供了一个估计的参数b从13 CO J=1-0谱线成像观测和灭绝映射的金牛座分子云，使用最近开发的技术，需要包含的信息只在投影列密度场计算σ ^{2}_{rho/ rho_{0} }。我们发现b ~ 0.48，这是符合典型的数值估计，是湍流驱动，包括螺线管和压缩模式的混合物的特点。更保守地，我们将b限制在0.3-0.8的范围内，这取决于亚分辨率结构的影响和扩散原子材料在柱密度预算中的作用。我们还报告了一个突破金牛座柱密度功率谱的规模为1 pc，并发现，打破与各向异性的功率谱。在13 CO和尘埃消光功率谱中观察到这种断裂，尽管13 CO和尘埃消光图之间存在详细的空间差异，但它们明显是相同的。[删节]
英文摘要：
Supersonic turbulence in molecular clouds is a key agent in generating density enhancements that may subsequently go on to form stars. The stronger the turbulence - the higher the Mach number - the more extreme the density fluctuations are expected to be. Numerical models predict an increase in density variance with rms Mach number of the form: sigma^{2}_{rho/rho_{0}} = b^{2}M^{2}, where b is a numerically-estimated parameter, and this prediction forms the basis of a large number of analytic models of star formation. We provide an estimate of the parameter b from 13CO J=1-0 spectral line imaging observations and extinction mapping of the Taurus molecular cloud, using a recently developed technique that needs information contained solely in the projected column density field to calculate sigma^{2}_{rho/rho_{0}}. We find b ~ 0.48, which is consistent with typical numerical estimates, and is characteristic of turbulent driving that includes a mixture of solenoidal and compressive modes. More conservatively, we constrain b to lie in the range 0.3-0.8, depending on the influence of sub-resolution structure and the role of diffuse atomic material in the column density budget. We also report a break in the Taurus column density power spectrum at a scale of ~1pc, and find that the break is associated with anisotropy in the power spectrum. The break is observed in both 13CO and dust extinction power spectra, which, remarkably, are effectively identical despite detailed spatial differences between the 13CO and dust extinction maps. [ abridged ]
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