有限厚度富气星系盘的结构形成：从盘到环
Structure Formation in Gas-Rich Galactic Discs with Finite Thickness: From Discs to Rings
摘要：
引力不稳定性在富气高红移盘星系的结构形成中起着重要的作用。在本文中，我们重新考虑轴对称扰动理论和由此产生的增长的结构，考虑到现实的厚度的光盘。在不稳定的制度，这对应于厚盘的Toomre参数低于临界值Q_0，crit = 0.696，我们发现一个增长最快的扰动波长，总是一个因素的1.93倍，比在经典的剃刀薄盘近似。该结果与所采用的圆盘高度无关，因此与温度和表面密度无关。为了检验分析理论，我们将其与具有典型垂直sech ^2密度分布的等温重力不稳定气体盘的高分辨率流体动力学模拟进行了比较，并研究了它分裂成环，然后分裂成致密的团块。在第一阶段，环的形式，组织自己离散，与当地增长最快的扰动波长对应的距离。我们发现，光盘scaleheight必须解决最初与五个或更多的网格单元，以保证适当的增长的环结构，这遵循的分析预测。这些环后来收缩成一条细而致密的线，同时从环间区域吸积更多的气体。正是这些密集的圆形细丝，随后分裂成大量的团块。与通常所假设的相反，团簇大小因此不直接由增长最快的波长决定。
英文摘要：
Gravitational instabilities play an important role in structure formation of gas-rich high-redshift disc galaxies. In this paper, we revisit the axisymmetric perturbation theory and the resulting growth of structure by taking the realistic thickness of the disc into account. In the unstable regime, which corresponds for thick discs to a Toomre parameter below the critical value Q_0,crit = 0.696, we find a fastest growing perturbation wavelength that is always a factor 1.93 times larger than in the classical razor-thin disc approximation. This result is independent of the adopted disc scaleheight and by this independent of temperature and surface density. In order to test the analytical theory, we compare it with a high-resolution hydrodynamical simulation of an isothermal gravitationally unstable gas disc with the typical vertical sech^2 density profile and study its break up into rings that subsequently fragment into dense clumps. In the first phase, rings form, that organize themselves discretely, with distances corresponding to the local fastest growing perturbation wavelength. We find that the disc scaleheight has to be resolved initially with five or more grid cells in order to guarantee proper growth of the ring structures, which follow the analytical prediction. These rings later on contract to a thin and dense line, while at the same time accreting more gas from the inter-ring region. It is these dense, circular filaments, that subsequently fragment into a large number of clumps. Contrary to what is typically assumed, the clump sizes are therefore not directly determined by the fastest growing wavelength.
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