Department of Physics and Astronomy, The University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Nature. 2011 Sep 14;477(7364):301-3. doi: 10.1038/nature10417.
Like many galaxies of its size, the Milky Way is a disk with prominent spiral arms rooted in a central bar, although our knowledge of its structure and origin is incomplete. Traditional attempts to understand our Galaxy's morphology assume that it has been unperturbed by major external forces. Here we report simulations of the response of the Milky Way to the infall of the Sagittarius dwarf galaxy (Sgr), which results in the formation of spiral arms, influences the central bar and produces a flared outer disk. Two ring-like wrappings emerge towards the Galactic anti-Centre in our model that are reminiscent of the low-latitude arcs observed in the same area of the Milky Way. Previous models have focused on Sgr itself to reproduce the dwarf's orbital history and place associated constraints on the shape of the Milky Way gravitational potential, treating the Sgr impact event as a trivial influence on the Galactic disk. Our results show that the Milky Way's morphology is not purely secular in origin and that low-mass minor mergers predicted to be common throughout the Universe probably have a similarly important role in shaping galactic structure.
像许多大小相似的星系一样，银河系是一个带有突出旋臂的盘状星系，其旋臂的根部是一个中央棒状结构，但我们对银河系的结构和起源的了解并不完整。传统上，人们试图通过理解银河系的形态来假设它没有受到外部主要力量的干扰。在这里，我们报告了对银河系对 Sagittarius 矮星系（Sgr）的引力作用的模拟，结果表明银河系形成了旋臂，影响了中央棒状结构，并产生了向外扩展的盘状结构。在我们的模型中，两个环状的包裹物出现在银河系的反中心方向，这让人联想到在银河系同一区域观察到的低纬度弧形结构。以前的模型主要集中在 Sgr 本身，以重现矮星系的轨道历史，并对银河系引力势的形状施加相关限制，将 Sgr 的撞击事件视为对银河系盘的微不足道的影响。我们的结果表明，银河系的形态并非纯粹是由长期演化引起的，而且在整个宇宙中预测普遍存在的低质量的次要合并可能在塑造星系结构方面也具有同样重要的作用。
