论文标题
螺旋星系中两个组分分子盘的理论建模
Theoretical modelling of two-component molecular discs in spiral galaxies
论文作者
论文摘要
由于螺旋星系中分子盘的最新观察表明，存在弥漫性，低密度厚的分子盘以及突出的薄盘，我们研究了该厚光盘的观察性特征，理论上通过在附近八个螺旋星系的样品中对两个组分的分子盘进行了建模。假设有盛行的静水平衡，我们建立并求解了关节泊松的玻尔兹曼方程，以估计样品星系中分子气和分子尺度的三维分布。发现两个组分分子盘中的分子尺度高度在50-300美元之间变化，高于单一组件盘中的分子盘高度。我们发现，根据假定的厚盘分子气分，该比例高度可能会显着变化。我们还发现，分子气体的耀斑是半径的函数，并遵循一个紧密的指数定律，比例长度为$ \左（0.48 \ pm 0.01 \ right）r_ {25} $。我们使用密度溶液来生成柱密度图和光谱立方体，以检查理想的观察条件，以鉴定星系中的厚分子盘。我们发现，除非分子盘是一个边缘系统，并且以高空间分辨率（$ \ lyssim 100 $ PC）成像，否则很难在柱密度图中识别厚的分子盘。光谱分析进一步表明，在中等至高倾斜度（$ i \ gtrsim 40^o $）时，光谱宽扩展可以虚拟地将两组盘的签名引入单个组件盘的频谱立方体。因此，我们得出的结论是，以高空间分辨率成像的低倾斜分子盘将成为识别星系中厚分子盘的理想位点。
As recent observations of the molecular discs in spiral galaxies point to the existence of a diffuse, low-density thick molecular disc along with the prominent thin one, we investigate the observational signatures of this thick disc by theoretically modelling two-component molecular discs in a sample of eight nearby spiral galaxies. Assuming a prevailing hydrostatic equilibrium, we set up and solved the joint Poisson's-Boltzmann equation to estimate the three-dimensional distribution of the molecular gas and the molecular scale height in our sample galaxies. The molecular scale height in a two-component molecular disc is found to vary between $50-300$ pc, which is higher than what is found in a single-component disc. We find that this scale height can vary significantly depending on the assumed thick disc molecular gas fraction. We also find that the molecular gas flares as a function of the radius and follows a tight exponential law with a scale length of $\left(0.48 \pm 0.01 \right) r_{25}$. We used the density solutions to produce the column density maps and spectral cubes to examine the ideal observing conditions to identify a thick molecular disc in galaxies. We find that unless the molecular disc is an edge-on system and imaged with a high spatial resolution ($\lesssim 100$ pc), it is extremely hard to identify a thick molecular disc in a column density map. The spectral analysis further reveals that at moderate to high inclination ($i \gtrsim 40^o$), spectral broadening can fictitiously introduce the signatures of a two-component disc into the spectral cube of a single-component disc. Hence, we conclude that a low inclination molecular disc imaged with high spatial resolution would serve as the ideal site for identifying the thick molecular disc in galaxies.
