The origin of galactic disks

这个提议的主题集中在所谓的宇宙学角动量问题上。在盘状星系形成的数值模拟中，落入暗物质晕中的气体失去了角动量，这导致盘状星系的尺度长度与观测结果相比太小。我们想研究这个问题是否源于光滑粒子流体动力学（SPH）的数值问题。在以前的研究中，有人指出，在介质密度对比的开尔文亥姆霍兹不稳定性（KHI）是完全抑制由于一个不正确的平滑过程。因此，该项目的主要目标是改进SPH形式主义，以便对星系的演化进行逼真的宇宙学模拟。KHI的影响将根据冷气体云落入包含热气日冕的大型暗物质晕的例子更详细地说明。通过应用宇宙学模拟的问题将调查是否人为抑制的KHI导致角动量问题，以及是否可以防止这个问题使用改进的SPH算法。

The subject of this proposal focuses on the so called cosmological angular momentum problem. In numerical simulations of the formation of disk galaxies gas infalling into dark matter halos loses its angular momentum which results in disks with scale-lengths that are too small if compared to observations. We want to study if this problem arises from numerical problems connected with smooth particle hydrodynamics (SPH). In previous studies it was pointed out that in media with density contrasts the Kelvin Helmholtz instability (KHI) is completely suppressed due to an incorrect smoothing procedure. The key goal of this project is therefore to improve the SPH formalism in order to perform realistic cosmological simulations on the evolution of galaxies. The influence of the KHI will be specified in more detail based on the example of infalling cold gas clouds into large dark matter halos, that contain a hot gaseous corona. By applying cosmological simulations the question will be investigated whether an artificial suppression of the KHI causes the angular momentum problem and whether this problem can be prevented using an improved SPH algorithm.