恒星形成分子云中的“真”柱密度分布
The "True" Column Density Distribution in Star-Forming Molecular Clouds
摘要：
我们使用COMPRESSION调查的英仙座恒星形成区域的观测，以评估和相互比较三种方法测量柱密度的分子云：消光映射（NIR）;热发射映射（FIR）;和映射的CO同位素的强度。所有三种示踪剂显示的结构在形态上相似，但存在重要差异。基于尘埃的测量给出了类似的，对数正态分布的整个英仙座地区，一旦仔细校准校正。我们还比较了尘埃和气体为基础的柱密度分布的物理意义的子区域英仙座，我们发现这些地区的分布显着变化。即使我们已经使用了12 CO数据来估计激发温度，我们已经纠正了不透明度，13 CO地图似乎无法得到列分布一致类似于从尘埃措施。我们已经编辑了B星HD 278942周围的外壳的效果。在壳层的内部和与分子云重叠的部分，似乎缺乏13 CO，可能是由于13 CO还没有时间在这个年轻的结构中形成，和/或分子云中的13 CO被破坏。我们的结论是，使用无论是灰尘或气体的柱密度的措施，而不极端注意校准和文物是更危险的，甚至比专家通常可能承认。而且，使用13 CO来详细追踪总柱密度，即使在适当校准之后，由于阈值、耗尽和不透明度效应，在实用性上也是不可避免地受限的。如果一个人的主要目标是绘制气柱密度图，那么尘埃灭绝似乎是最好的探测器。列密度示踪剂之间的线性拟合，量化使用一个示踪剂（与其他相比）的固有不确定性。[删节]
英文摘要：
We use the COMPLETE Survey's observations of the Perseus star-forming region to assess and intercompare three methods for measuring column density in molecular clouds: extinction mapping (NIR); thermal emission mapping (FIR); and mapping the intensity of CO isotopologues. The structures shown by all three tracers are morphologically similar, but important differences exist. Dust-based measures give similar, log-normal, distributions for the full Perseus region, once careful calibration corrections are made. We also compare dust- and gas-based column density distributions for physically-meaningful sub-regions of Perseus, and we find significant variations in the distributions for those regions. Even though we have used 12CO data to estimate excitation temperatures, and we have corrected for opacity, the 13CO maps seem unable to give column distributions that consistently resemble those from dust measures. We have edited out the effects of the shell around the B-star HD 278942. In that shell's interior and in the parts where it overlaps the molecular cloud, there appears to be a dearth of 13CO, likely due either to 13CO not yet having had time to form in this young structure, and/or destruction of 13CO in the molecular cloud. We conclude that the use of either dust or gas measures of column density without extreme attention to calibration and artifacts is more perilous than even experts might normally admit. And, the use of 13CO to trace total column density in detail, even after proper calibration, is unavoidably limited in utility due to threshold, depletion, and opacity effects. If one's main aim is to map column density, then dust extinction seems the best probe. Linear fits amongst column density tracers are given, quantifying the inherent uncertainties in using one tracer (when compared with others). [abridged]
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