arXiv 1202.52802012-02-23astro-ph.COastro-ph.GA

星系潮汐尾的对称性和标度

The symmetries and scaling of tidal tails in galaxies

Curtis Struck, Beverly J. Smith

备注：: MNRAS accepted, 24 pages, 21 figures
DOI：: 10.1111/j.1365-2966.2012.20798.x

摘要：

我们提出了星系碰撞中脉冲扰动引起的潮汐尾和相关结构的形成和演化的解析模型。由于周转近似对于大的径向偏移是无效的，我们使用我们称之为p-椭圆的轨道方程。这些已被证明是提供准确的表示轨道的幂律晕势。在纯潮汐扰动的情况下，所产生的潮汐尾具有简单的结构。缩放的最大长度和其他特性的潮汐振幅和幂律势的指数的函数进行了说明。分析模型表明，方位角焦散线（轨道交叉区）一般产生在这些尾巴在一个固定的方位角相对于最接近的点。在其底部具有高阶焦散线的长尾也在较大的振幅下产生。分析扩展到非线性扰动和多次遭遇，打破潮汐扰动的对称性。由于非线性项的强度是不同的，所得到的形式的结构不同，从对称的尾巴单臂羽流。有两个或两个以上的脉冲干扰的情况下，也被认为是最简单的分析模型之间的区别逆行和逆行的遭遇。潮汐矮星系的尾巴末端形成的一个具体机制建议作为一个结果的共振效应在长期的遭遇。与Arp Atlas系统的定性比较表明，在实际系统中实现了极限分析情况。我们确定了几个ARP系统，可能有燕尾焦散，耗散气体流汇聚，并触发恒星形成。紫外线和光学图像揭示了这些“铰链丛”位置的年轻恒星的发光结。

英文摘要：

(Abriged) We present analytic models for the formation and evolution of tidal tails and related structures following impulsive disturbances in galaxy collisions. Since the epicyclic approximation is not valid for large radial excursions, we use orbital equations of the form we call p-ellipses. These have been shown to provide accurate representations of orbits in power-law halo potentials. In the case of a purely tidal disturbance the resulting tidal tails have simple structure. Scalings for their maximum lengths and other characteristics as functions of the tidal amplitude and the exponent of the power-law potentials are described. The analytic model shows that azimuthal caustics (orbit crossing zones) are produced generically in these tails at a fixed azimuth relative to the point of closest approach. Long tails, with high order caustics at their base are also produced at larger amplitudes. The analysis is extended to nonlinear disturbances and multiple encounters, which break the symmetries of tidal perturbations. As the strength of the nonlinear terms is varied the structure of the resulting forms varies from symmetric tails to one-armed plumes. Cases with two or more impulse disturbances are also considered as the simplest analytic models distinguishing between prograde and retrograde encounters. A specific mechanism for the formation of tidal dwarf galaxies at the end of tails is suggested as a consequence of resonance effects in prolonged encounters. Qualitative comparisons to Arp Atlas systems suggest that the limiting analytic cases are realized in real systems. We identify a few Arp systems which may have swallowtail caustics, where dissipative gas streams converge and trigger star formation. UV and optical images reveal luminous knots of young stars at these 'hinge clump' locations.

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