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arXiv 1601.06115astro-ph.GA
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尖突星系中棒的形成机制

On the bar formation mechanism in galaxies with cuspy bulges

Evgeny Polyachenko, Peter Berczik, Andreas Just

摘要:

我们表明,通过数值模拟,一个纯粹的恒星动力学模型组成的指数盘,一个尖锐的隆起,和NFW晕与银河系相关的参数是受酒吧的形成。考虑到有限的磁盘厚度,酒吧的形成可以解释通常的酒吧不稳定性,尽管存在的内部Lindblad共振,这被认为是阻尼任何全球模式。研究了用一个固定的外部轴对称势(刚性模型)代替活的晕和球的效果。它示出,而杆不稳定的e-折叠时间显着增加(从250到500万年),酒吧模式的速度几乎保持不变。对于后者,我们的平均值为55公里/秒/千秒差距同意的假设,大力士流在太阳附近是一个印记的酒吧-光盘相互作用在外部Lindblad共振的酒吧。垂直平均的径向力在中心盘区域的特征尺度长度相比,使我们能够重现的酒吧模式的速度和增长率的刚性模型,使用正常模式分析的线性扰动理论在剃刀薄盘。模式分析预测,随着圆盘质量的减少,e-折叠时间的强烈增加表明,类似于银河系的星系中的酒吧最近才形成。

英文摘要:

We show by numerical simulations that a purely stellar dynamical model composed of an exponential disc, a cuspy bulge, and an NFW halo with parameters relevant to the Milky Way Galaxy is subject to bar formation. Taking into account the finite disc thickness, the bar formation can be explained by the usual bar instability, in spite of the presence of an inner Lindblad resonance, that is believed to damp any global modes. The effect of replacing the live halo and bulge by a fixed external axisymmetric potential (rigid models) is studied. It is shown that while the e-folding time of bar instability increases significantly (from 250 to 500 Myr), the bar pattern speed remains almost the same. For the latter, our average value of 55 km/s/kpc agrees with the assumption that the Hercules stream in the solar neighbourhood is an imprint of the bar--disc interaction at the outer Lindblad resonance of the bar. Vertical averaging of the radial force in the central disc region comparable to the characteristic scale length allows us to reproduce the bar pattern speed and the growth rate of the rigid models, using normal mode analysis of linear perturbation theory in a razor thin disc. The strong increase of the e-folding time with decreasing disc mass predicted by the mode analysis suggests that bars in galaxies similar to the Milky Way have formed only recently.

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