Milgromian动力学中的Local Group计时。z>0.8时的过去Milky Way -仙女座遭遇
Local Group timing in Milgromian dynamics. A past Milky Way-Andromeda encounter at z>0.8
摘要：
本机组计时一直是失踪的质量问题的第一个历史性的探索之一。虽然现代宇宙学探测表明，纯重子动力学在最大尺度上是不够的，但附近的星系和小星系群一直遵守米尔格罗姆的MOND定律，这意味着小尺度的动力学可能完全由重子预测。在这里，我们调查本地集团的时间在这种背景下Milgromian动态。利用最新观测到的仙女座星云和麦哲伦星云的自行和径向速度，利用Milgromian二体运动方程，对它们的轨道进行了积分。我们发现，与目前测量的自行和径向速度的M31，MOND将意味着银河系和M31出生后，首先通过哈勃膨胀分开，但随后必然会再次被吸引Milgromian引力吸引，并有一个过去的飞行相遇之前来到他们现在的位置。这种遭遇很可能发生在7到11 Gyr之前（0.8<z<3）。没有暗物质晕及其相关的动力学摩擦是这种近距离接触不触发合并的必要条件。因此，从在本星系群规模上证伪或证明米尔格罗米亚动力学的观点来看，能够排除或支持这种过去相遇的观测论证是非常重要的。有趣的是，最接近的相遇是足够小的（<55 kpc），对盘动力学有严重的影响，包括厚盘的形成，以及两个星系的卫星系统。卫星星系和年轻的晕状球状星团的年龄都与这些天体在这次相遇中诞生的年龄相一致，它们都形成了银河系周围巨大的极地结构。
英文摘要：
The Local Group timing has been one of the first historical probes of the missing mass problem. Whilst modern cosmological probes indicate that pure baryonic dynamics is not sufficient on the largest scales, nearby galaxies and small galaxy groups persistently obey Milgrom's MOND law, which implies that dynamics at small scales is possibly entirely predicted by the baryons. Here, we investigate the Local Group timing in this context of Milgromian dynamics. Making use of the latest measured proper motions and radial velocities for Andromeda and the Magellanic clouds, we integrate backwards their orbits by making use of the Milgromian two-body equation of motion. We find that, with the currently measured proper motions and radial velocity of M31, MOND would imply that the Milky Way and M31 first moved apart via Hubble expansion after birth, but then necessarily got attracted again by the Milgromian gravitational attraction, and had a past fly-by encounter before coming to their present positions. This encounter would most probably have happened 7 to 11 Gyr ago (0.8<z<3). The absence of a dark matter halo and its associated dynamical friction is necessary for such a close encounter not to trigger a merger. Observational arguments which could exclude or favour such a past encounter would thus be very important in view of falsifying or vindicating Milgromian dynamics on the scale of the Local Group. Interestingly, the closest approach of the encounter is small enough (<55 kpc) to have severe consequences on the disk dynamics, including perhaps thick disk formation, and on the satellite systems of both galaxies. The ages of the satellite galaxies and of the young halo globular clusters, all of which form the vast polar structure around the Milky Way, are consistent with these objects having been born in this encounter.
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