大质量恒星主导了星系的物理与化学演化。分子云中稠密云核的密度分布是恒星形成的重要初始条件，恒星形成理论提出云核体密度分布随距离应呈幂指数衰减，然而由于观测精度所限，该结论一直未能在大质量恒星样本中得到证实。近期，Herschel空间望远镜的银道面巡天项目Hi-GAL得到了远红外多波段图像，人们基于此导出了全银道面的柱密度全图，为本文的工作提供了基础。在本文中，我选取了10个处于prestellar阶段（即尚未形成原恒星）、20个处于protostellar阶段（即已经形成原恒星）的大质量恒星形成区，对它们的柱密度、体密度结构特征分别进行了研究。

       通过与Dapp & Basu模型拟合，得到两类演化阶段的恒星形成区在柱密度上分别具有以下特征：对于处于prestellar阶段的形成区，其柱密度以显著慢于幂指数衰减的速率从中心缓慢下降，且在截止半径处存在不明显的快速衰减；处于protostellar阶段的形成区呈现出了两类柱密度结构特征，一类按幂指数规律快速下降；另一类随距离减小的趋势与prestellar阶段类似。同时，protostellar阶段形成区的柱密度降低速率在整体上均比prestellar阶段更快。

       进一步假定恒星形成区的数量体密度分布形式为n∝r^(?p)，通过拟合获得两类演化阶段体密度结构中随距离按幂指数关系减小部分的衰减幂次，分别为未形成原恒星区域p=1.91±0.2，已形成原恒星区域p=1.96±0.4，因此二者体密度结构随距离衰减部分的趋势无显著不同。

Massive stars dominate the physical and chemical evolution of galaxies. Density distribution of dense cores embedded in molecular clouds provides crucial initial condition for star formation theories, which suggests that the density distribution of dense cores should decay exponentially with distance. However, due to limitation on observational accuracy, this conclusion has not been confirmed so far in the sample of massive star forming regions. Recently, the Herschel Space Telescope's galactic plane survey Hi-GAL released far-infrared multi-band images, based on which people derived a column density map covering the full galactic plane, providing the basis for the work of this paper. In this work, I selected 10 prestellar regions and 20 protostellar regions, studied the characteristics of their column density structure and volume density structure respectively.

By fitting observed column density data with the Dapp & Basu model, I found that column density structures of star forming regions under this two evolutionary stages have the following characteristics respectively: for prestellar regions, column density decline slowly from the center at a rate significantly slower than power exponential decay, and there is no obvious cutoff effect near the edge; protostellar regions show two types of column density structure characteristics, one of which decreases rapidly by power exponential law, the other kind decreases in a similar trend to prestellar regions. At the same time, column density decreases faster in protostellar region than in prestellar region.

Taking a step further, while assuming the volume density distribution follows the form of n∝r^(?p), I obtained the power index of the two evolutionary stages: p=1.91±0.2 for prestellar sources, and p =1.96±0.4 for protostellar sources. There is no significant difference between the volume density characteristics of the two evolutionary stages.