在传统和修正动力学中矮球状星系中动力化石的生存
The survival of dynamical fossils in dwarf spheroidal galaxies in conventional and modified dynamics
摘要：
非束缚密度子结构对轨道混合的生存对潜在的引力势的斜率施加了很强的约束，并提供了一个新的测试修改的重力。在这里，我们调查的解释，小熊座（UMi）矮球状星系的恒星团是一个“动力化石”是否符合修正牛顿动力学（MOND）。对于UMi质量模型推断拟合的速度色散曲线，恒星团周围的第二个高峰UMi擦除非常迅速，在1.25 Gyr（6.5轨道），即使包括自引力。我们发现，即使在更慷慨的条件下，团块也很难存活超过2 Gyr。替代方案，可能会导致一个运动学冷块进行了讨论，但到目前为止，没有一个被发现是完全令人满意的。我们的结论是，在UMi冷团构成了一个挑战，LambdaCDM和MOND。
英文摘要：
The survival of unbound density substructure against orbital mixing imposes strong constraints on the slope of the underlying gravitational potential and provides a new test on modified gravities. Here we investigate whether the interpretation that the stellar clump in Ursa Minor (UMi) dwarf spheroidal galaxy is a `dynamical fossil' is consistent with Modified Newtonian dynamics (MOND). For UMi mass models inferred by fitting the velocity dispersion profile, the stellar clump around the second peak of UMi is erased very rapidly, within 1.25 Gyr (6.5 orbits), even with the inclusion of self-gravity. We find that the clump can hardly survive for more than 2 Gyr even under more generous conditions. Alternative scenarios which could lead to a kinematically cold clump are discussed but, so far, none of them were found to be fully satisfactory. Our conclusion is that the cold clump in UMi poses a challenge for both LambdaCDM and MOND.
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