标题： 分子云的结构：II - 柱密度和质量分布 显示英文标题

标题： The Structure of Molecular Clouds: II - Column Density and Mass Distributions

摘要： 恒星的形成与它们的母分子云的结构密不可分。 在这里，我们选取了一些附近的巨大分子云（GMCs），并分析它们的柱密度和质量分布。 这项研究基于四张新的全天中值颜色过量消光图，这些图是通过2MASS确定的。 这四张图覆盖了八倍的空间分辨率范围。 这使我们能够在0.1pc的共同空间尺度上确定云的属性，同时研究云属性的尺度依赖性。 我们发现，云的低柱密度和湍流主导部分可以用对数正态分布很好地拟合。 然而，在所有研究的云中，超过一个普遍的消光阈值6.0 \pm 1.5mag A_V 的部分存在超出对数正态分布的物质。 这部分物质代表当前参与恒星形成的云的部分，因此由引力主导。 它对云总质量的贡献范围从0.1%到10%，跨越两个数量级。 这意味着我们的云样本涵盖了GMC演化过程中的不同阶段。 此外，我们发现如果仅分析高消光物质，云之间的柱密度和质量分布非常相似。 另一方面，如果仅考虑低消光、湍流主导的区域，则分布之间存在显著差异。 这表明湍流特性因云的环境不同而有所差异。 然而，没有发现对恒星形成的主要模式（聚集或孤立）有显著影响。 此外，云中积极参与恒星形成的部分仅由引力决定，柱密度和质量分布未被局部反馈过程显著改变。 显示英文摘要

摘要： The formation of stars is inextricably linked to the structure of their parental molecular clouds. Here we take a number of nearby giant molecular clouds (GMCs) and analyse their column density and mass distributions. This investigation is based on four new all-sky median colour excess extinction maps determined from 2MASS. The four maps span a range of spatial resolution of a factor of eight. This allows us to determine cloud properties at a common spatial scale of 0.1pc, as well as to study the scale dependence of the cloud properties. We find that the low column density and turbulence dominated part of the clouds can be well fit by a log-normal distribution. However, above a universal extinction threshold of 6.0 \pm 1.5mag A_V there is excess material compared to the log-normal distribution in all investigated clouds. This material represents the part of the cloud that is currently involved in star formation, and thus dominated by gravity. Its contribution to the total mass of the clouds ranges over two orders of magnitude from 0.1 to 10%. This implies that our clouds sample various stages in the evolution of GMCs. Furthermore, we find that the column density and mass distributions are extremely similar between clouds if we analyse only the high extinction material. On the other hand, there are significant differences between the distributions if only the low extinction, turbulence dominated regions are considered. This shows that the turbulent properties differ between clouds depending on their environment. However, no significant influence on the predominant mode of star formation (clustered or isolated) could be found. Furthermore, the fraction of the cloud actively involved in star formation is only governed by gravity, with the column density and mass distributions not significantly altered by local feedback processes.