Andromeda II as a merger remnant
Andromeda II as a merger remnant
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仙女座二号是合并的残余物
DOI：
10.1093/mnrasl/slu128
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发表时间：
2014
影响因子：
4.8
通讯作者：
M. Semczuk
中科院分区：
文献类型：
--
作者：
E. Lokas;I. Ebrová;A. Pino;M. Semczuk
使用N-体模拟，我们研究的起源，最近发现的运动学数据和II，一个dSph卫星的M31的长轴旋转。我们提出了一个演化模型的起源和II涉及合并两个盘状矮星系的结构参数不同，只有在他们的磁盘尺度长度。这两颗矮星被放置在一个径向轨道上，它们的角动量相对于轨道平面倾斜45度，相对于彼此倾斜90度。经过5 Gyr的演化，合并的残余物形成了一个稳定的三轴星系，只围绕最长轴旋转。这种旋转的起源自然被解释为由于初始构型的对称性，这导致了沿合并方向的角动量分量沿着守恒。来自两颗矮星的恒星显示出明显不同的表面密度分布，同时具有非常相似的运动学，与And II中单独恒星种群的性质一致。我们还研究了另一种方案的形成和II，通过潮汐搅拌的盘状矮星系。虽然在这个模型中，内禀自转是盘初始自转的残余，但它主要是围绕恒星组成部分的最短轴。围绕最长轴的旋转只是偶尔引起的，并且保持比系统的速度色散小得多。我们的结论是，虽然潮汐起源的速度分布和II不能被排除在外，它是更自然地解释的情况下，涉及过去的合并事件。因此，原则上，在本星系群及更远的dSph星系中，长轴自转的存在可以作为它们历史上主要合并的指标，甚至可以作为区分它们形成的两种情况的一种方式。
Using N-body simulations we study the origin of prolate rotation recently detected in the kinematic data for And II, a dSph satellite of M31. We propose an evolutionary model for the origin of And II involving a merger between two disky dwarf galaxies whose structural parameters differ only in their disk scale lengths. The dwarfs are placed on a radial orbit towards each other with their angular momenta inclined by 45 deg to the orbital plane and by 90 deg with respect to each other. After 5 Gyr of evolution the merger remnant forms a stable triaxial galaxy with rotation only around the longest axis. The origin of this rotation is naturally explained as due to the symmetry of the initial configuration which leads to the conservation of angular momentum components along the direction of the merger. The stars originating from the two dwarfs show significantly different surface density profiles while having very similar kinematics in agreement with the properties of separate stellar populations in And II. We also study an alternative scenario for the formation of And II, via tidal stirring of a disky dwarf galaxy. While intrinsic rotation occurs naturally in this model as a remnant of the initial rotation of the disk, it is mostly around the shortest axis of the stellar component. The rotation around the longest axis is induced only occasionally and remains much smaller that the system's velocity dispersion. We conclude that although tidal origin of the velocity distribution in And II cannot be excluded, it is much more naturally explained within the scenario involving a past merger event. Thus, in principle, the presence of prolate rotation in dSph galaxies of the Local Group and beyond may be used as an indicator of major mergers in their history or even as a way to distinguish between the two scenarios of their formation.