arXiv 1109.26222011-09-12astro-ph.GA

银盘中准径向密度波的微扰分析

A perturbative analysis of Quasi-Radial density waves in galactic disks

X. Hernandez, I. Puerari

备注：: 12 pages, 7 figures

摘要：

对盘星系密度波的理论理解始于经典的紧缠绕微扰的WKB微扰分析，其关键假设是密度波产生的势近似为径向。尽管存在一些警告，但上述内容在帮助理解模拟和观测星系方面起到了有价值的指导作用。在真实星系中观察到的螺旋或条形图案经常与紧缠绕假设仅在边缘上一致，实际上经常完全不一致。在这里，我们推导出一个互补的制定的问题，通过处理准径向密度波的简化假设下的线性制度。假设密度波的势近似切向，导出了相应的色散关系。我们得到的准径向密度波的发病，这使得一个清晰的理解，增加了稳定性的高阶模式，它出现在逐渐变大的半径，经常看到在真实的星系的不稳定性标准。该理论自然地为这些臂产生一系列的模式速度，这些模式速度似乎受到条件$Ω_{p}<Ω_{0} \pm κ/m$的约束。对于中心地区的星系，固体旋转曲线可能适用，我们发现弱酒吧在振荡制度与各种模式的速度，包括反旋转的，和预测$Ω_{p}$向中心增加，看到在快速旋转的酒吧内的酒吧的一些数值模拟。我们补充这项研究与详细的数值模拟星系盘和仔细的傅立叶分析的紧急扰动，支持提出的理论。

英文摘要：

The theoretical understanding of density waves in disk galaxies starts from the classical WKB perturbative analysis of tight-winding perturbations, the key assumption being that the potential due to the density wave is approximately radial. The above has served as a valuable guide in aiding the understanding of both simulated and observed galaxies, in spite of a number of caveats being present. The observed spiral or bar patterns in real galaxies are frequently only marginally consistent with the tight-winding assumption, often in fact, outright inconsistent. Here we derive a complementary formulation to the problem, by treating quasi-radial density waves under simplified assumptions in the linear regime. We assume that the potential due to the density wave is approximately tangential, and derive the corresponding dispersion relation of the problem. We obtain an instability criterion for the onset of quasi-radial density waves, which allows a clear understanding of the increased stability of the higher order modes, which appear at progressively larger radii, as often seen in real galaxies. The theory naturally yields a range of pattern speeds for these arms which appears constrained by the condition $Ω_{p}<Ω_{0} \pm κ/m$. For the central regions of galaxies where solid body rotation curves might apply, we find weak bars in the oscillatory regime with various pattern speeds, including counter rotating ones, and a prediction for $Ω_{p}$ to increase towards the centre, as seen in the rapidly rotating bars within bars of some numerical simulations. We complement this study with detailed numerical simulations of galactic disks and careful Fourier analysis of the emergent perturbations, which support the theory presented.

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