缓慢破碎的波浪：潮汐诱导螺旋结构的寿命
Slowly Breaking Waves: The Longevity of Tidally Induced Spiral Structure
摘要：
我们已经发现了长寿命的波在两套数值模型的快速（边缘绑定或未绑定）飞越星系碰撞，独立进行了两个不同的代码。在这两个模拟集的螺旋碰撞诱导酒吧形成的结果。虽然随着时间的推移，波的出现有变化，但它们不会像文献中描述的其他情况那样消失和反复出现。我们还提出了一个分析理论，可以占波的结构，而不是传播的瞬变，也不是作为一个固定的模式传播通过光盘。当这些波通过圆盘传播时，它们由脉冲扰动引发的相干振荡维持。具体地说，分析理论认为，它们是在扰动后追求相关周转轨道的恒星合奏中的焦散波。这个理论是Struck和他的合作者为碰撞的环形星系所发展的理论的延伸。这些模型表明，这种类型的波可能会持续几个陀螺仪，和星系的相互作用发生在可比的时间尺度上，因此由该机制产生的波可以在观测到的螺旋中得到很好的体现。特别是，这种机制可以解释在一些附近的早期星系中看到的紧密缠绕的螺旋，并且可能是长寿的螺旋。这些螺旋也可能在星系群和星系团中很常见，星系之间的快速相遇相对频繁。然而，随着螺旋变得紧密缠绕，并发展到适度的振幅，除非它们在附近，否则它们可能难以分辨。尽管如此，这种效应可能是星系骚扰导致的几个过程之一，并通过波增强的恒星形成促成了布彻-奥姆勒效应。
英文摘要：
We have discovered long-lived waves in two sets of numerical models of fast (marginally bound or unbound) flyby galaxy collisions, carried out independently with two different codes. In neither simulation set are the spirals the result of a collision-induced bar formation. Although there is variation in the appearance of the waves with time, they do not disappear and reform recurrently, as seen in other cases described in the literature. We also present an analytic theory that can account for the wave structure, not as propagating transients, nor as a fixed pattern propagating through the disc. While these waves propagate through the disc, they are maintained by the coherent oscillations initiated by the impulsive disturbance. Specifically, the analytic theory suggests that they are caustic waves in ensembles of stars pursuing correlated epicyclic orbits after the disturbance. This theory is an extension of that developed by Struck and collaborators for colliding ring galaxies. The models suggest that this type of wave may persist for a couple of Gyr., and galaxy interactions occur on comparable timescales, so waves produced by the mechanism may be well represented in observed spirals. In particular, this mechanism can account for the tightly wound, and presumably long-lived spirals, seen in some nearby early-type galaxies. These spirals are also likely to be common in groups and clusters, where fast encounters between galaxies occur relatively frequently. However, as the spirals become tightly wound, and evolve to modest amplitudes, they may be difficult to resolve unless they are nearby. Nonetheless, the effect may be one of several processes that result from galaxy harassment, and via wave-enhanced star formation contribute to the Butcher-Oemler effect.
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