用真实银河势对中心分子带的流体动力学模拟
Hydrodynamic simulations of the central molecular zone with realistic Galactic potential
摘要：
我们提出了流体动力学模拟的气体云流入从磁盘到几百秒差距的银河系区域。通过使用描述自洽银河系模拟的640万个恒星粒子的数千个多极展开，产生了包括现实银河系结构的引力势。我们发现，一个混合多极展开模型，两个不同的基组和厚盘校正，准确地再现了银河系的整体结构。通过非轴对称的细长棒和旋臂的银河系结构，盘中的气体云流入核区域并形成中心分子带（CMZ）样的核环。我们发现，核环的大小演变到约240 pc的T~1500万年，无论初始大小。对于大多数模拟运行，气体流入到核区域的速率被平衡到~0.02 Msun/yr。核环相对于银河系中心是偏心的，由于银河系模型的中心质量分布不平衡，因此核环的质量分布不对称。银河系模型的垂直不对称性也导致核环沿着银河平面倾斜。在第一个~ 1亿年期间，气体运动的垂直频率是轨道频率的两倍，因此投影的核环显示出扭曲的，无限大的形状。
英文摘要：
We present hydrodynamic simulations of gas clouds inflowing from the disk to a few hundred parsec region of the Milky Way. A gravitational potential is generated to include realistic Galactic structures by using thousands of multipole expansions that describe 6.4 million stellar particles of a self-consistent Galaxy simulation. We find that a hybrid multipole expansion model, with two different basis sets and a thick disk correction, accurately reproduces the overall structures of the Milky Way. Through non-axisymmetric Galactic structures of an elongated bar and spiral arms, gas clouds in the disk inflow to the nuclear region and form a central molecular zone (CMZ)-like nuclear ring. We find that the size of the nuclear ring evolves into ~240 pc at T~1500 Myr, regardless of the initial size. For most simulation runs, the rate of gas inflow to the nuclear region is equilibrated to ~0.02 M_sun/yr. The nuclear ring is off-centered, relative to the Galactic center, by the lopsided central mass distribution of the Galaxy model, and thus an asymmetric mass distribution of the nuclear ring arises accordingly. The vertical asymmetry of the the Galaxy model also causes the nuclear ring to be tilted along the Galactic plane. During the first ~100 Myr, the vertical frequency of the gas motion is twice that of the orbital frequency, thus the projected nuclear ring shows a twisted, infinity-like shape.
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