无耗散小合并中星系盘的慢化
The slowing down of galaxy disks in dissipationless minor mergers
摘要：
我们研究了无耗散小星系合并对残余角动量的影响。我们的模拟涵盖了一系列的初始轨道特征和系统组成的一个大质量的星系与一个大得多的（十分之一或二十分之一）无气体的同伴，它具有各种形态（盘或椭圆形）和中央重子质量浓度的凸起和磁盘合并。在合并过程中，轨道角动量重新分配到最终系统的内角动量中;主星系的内角动量可以根据轨道自旋矢量的相对方向（正向或逆行）增加或减少，而最初不旋转的暗物质晕总是获得角动量。恒星分量的比角动量总是减小而与卫星的轨道参数或形态无关，原星系自转速度的减小伴随着轨道各向异性的变化，合并残余物的自转速度与速度色散之比低于初始值这不仅是由于色散的增加，而且还由于盘旋转的减慢。我们简要地讨论了这些结果的天体物理学意义，这表明轻微的合并不会导致一个“随机行走”的过程中的恒星盘组成的星系的角动量，而是一个稳定的减少。较小的合并可能发挥作用，在生产中观察到的Tully-Fisher关系的S 0星系，以及在增加的速度色散和减少$v/σ$在大半径的S 0星系中观察到的大散射。
英文摘要：
We have investigated the impact of dissipationless minor galaxy mergers on the angular momentum of the remnant. Our simulations cover a range of initial orbital characteristics and the system consists of a massive galaxy with a bulge and disk merging with a much less massive (one-tenth or one-twentieth) gasless companion which has a variety of morphologies (disk- or elliptical-like) and central baryonic mass concentrations. During the process of merging, the orbital angular momentum is redistributed into the internal angular momentum of the final system; the internal angular momentum of the primary galaxy can increase or decrease depending on the relative orientation of the orbital spin vectors (direct or retrograde), while the initially non-rotating dark matter halo always gains angular momentum. The specific angular momentum of the stellar component always decreases independent of the orbital parameters or morphology of the satellite, the decrease in the rotation velocity of the primary galaxy is accompanied by a change in the anisotropy of the orbits, and the ratio of rotation speed to velocity dispersion of the merger remnant is lower than the initial value, not only due to an increase in the dispersion but also to the slowing -down of the disk rotation. We briefly discuss several astrophysical implications of these results, suggesting that minor mergers do not cause a "random walk" process of the angular momentum of the stellar disk component of galaxies, but rather a steady decrease. Minor mergers may play a role in producing the large scatter observed in the Tully-Fisher relation for S0 galaxies, as well as in the increase of the velocity dispersion and the decrease in $v/σ$ at large radii as observed in S0 galaxies.
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