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arXiv 1202.0358astro-ph.GA
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麦哲伦星云对银河系的影响:极移、弯曲和恒星形成历史

The influences of the Magellanic Clouds on the Galaxy: Pole shift, warp, and star formation history

Kenji Bekki

摘要:

我们研究了大麦云云首次进入银河系暗物质晕维里半径后,大麦哲伦云对银河系演化的影响。在我们的模型中,银河系和大麦哲伦星系都被建模为N体粒子,这样大麦哲伦星系对银河系的动力学影响就可以用完全自洽的方式来研究。此外,LMC的轨道参数是精心选择的,这样的LMC在银河系中的当前位置可以在我们的模拟中相当精确地再现。我们特别研究了大麦哲伦星系对岁差率、外部恒星和气体结构以及恒星形成历史的影响。我们的主要结果总结如下。LMC与星系的动力学相互作用可以引起星系的“极移”(或不规则的岁差/章动),典型的极移速率(点θ d)为~2度Gyr^{-1},对应于~ 7 μ asyr ^{-1}。LMC与银河系的相互作用导致了银河系外部翘曲结构的形成,从而证实了以往关于银河系翘曲形成的数值模拟结果。大麦哲伦星系与星系的相互作用还导致了外盘(R>20 kpc)旋臂的形成,并显著增加了外盘的垂直速度色散。银河系最后几个旋回的平均恒星形成率几乎不受大麦哲伦星云引潮力的影响。过去几个Gyr的太阳邻域(7 kpc < R < 10 kpc)恒星的年龄和金属丰度分布仅能被过去的LMC-星系相互作用轻微改变。基于这些结果,我们讨论了如何可能正在进行的银河系极移与10 μ asyr ^{-1}可以检测到未来的观测研究GAIA。

英文摘要:

We investigate how the Large Magellanic Cloud (LMC) influences the evolution of the Galaxy after the LMC enters into the virial radius of the dark matter halo of the Galaxy for the first time. Both the Galaxy and the LMC are modeled as N-body particles in our models so that the dynamical influences of the LMC on the Galaxy can be investigated in a fully self-consistent manner. Furthermore, the orbital parameters for the LMC are carefully chosen such that the present location of the LMC in the Galaxy can be rather precisely reproduced in our simulations. We particularly investigate the influences of the LMC on the precession rate, the outer stellar and gaseous structures, and the star formation history of the Galaxy. Our principals results are summarized as follows. The LMC-Galaxy dynamical interaction can cause "pole shift" (or irregular precession/nutation) of the Galaxy and the typical rate of pole shift (dot θ_{d}) is ~2 degree Gyr^{-1} corresponding to ~ 7 muas yr^{-1}. The LMC-Galaxy interaction induces the formation of the outer warp structures of the Galaxy, which thus confirms the results of previous numerical simulations on the formation of the Galactic warp. The LMC-Galaxy interaction also induces the formation of outer (R>20 kpc) spiral arms and increases the vertical velocity dispersion of the outer disk significantly. The mean star formation rate of the Galaxy for the last several Gyrs can be hardly influenced by the LMC's tidal force. The age and metallicity distribution of stars in the solar-neighborhood (7 kpc < R < 10 kpc) for the last several Gyr can be only slightly changed by the past LMC-Galaxy interaction. Based on these results, we discuss how the possible ongoing Galactic pole shift with 10 muas yr^{-1} can be detected by future observational studies by GAIA.

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