arXiv 2004.130562020-04-27astro-ph.GA

旋涡星系中双组分分子盘的理论模拟

Theoretical modelling of two-component molecular discs in spiral galaxies

Narendra Nath Patra

备注：: Accepted for publication in A&A
DOI：: 10.1051/0004-6361/201936483

摘要：

由于最近的观察螺旋星系中的分子盘指出存在一个弥漫的，低密度的厚分子盘以及突出的薄的，我们调查的观测签名，这个厚盘的理论模型的两个组件的分子盘在附近的8个螺旋星系的样本。假设一个流行的流体静力平衡，我们建立和解决联合泊松-玻尔兹曼方程估计的三维分布的分子气体和分子尺度的高度在我们的样本星系。在一个双组分分子光盘的分子尺度高度之间变化$50-300$ PC，这是高于在一个单组分光盘中发现的。我们发现，这一规模的高度可以显着变化，这取决于假设的厚盘分子气体分数。我们还发现，分子气体耀斑作为半径的函数，并遵循紧指数律与尺度长度为$\left(0.48 \pm 0.01 \right) r_{25}$。我们使用密度解来产生柱密度图和光谱立方体，以检查理想的观测条件来识别星系中的厚分子盘。我们发现，除非分子盘是一个边缘上的系统，并与高空间分辨率（$\lesssim 100$ pc）成像，这是非常困难的，以确定一个厚的分子盘在列密度图。光谱分析进一步揭示，在中等到高倾角（$i \gtrsim 40^o$），光谱展宽可以虚构地引入一个单组分光盘的光谱立方体的双组分光盘的签名。因此，我们的结论是，低倾角分子盘成像的高空间分辨率将作为理想的网站，以确定在星系中的厚分子盘。

英文摘要：

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.

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