Recent proper-motion observations indicate that the Magellanic Clouds are leading the Magellanic Stream. Although the direction of this motion is in agreement with that expected from theoretical models for the dynamics of the Clouds and the origin of the Stream, its magnitude is considerably smaller than that predicted. We reexamine the original conjecture that the Galaxy, during the past 14 x 10~9 yr, has tidally disrupted the LMC-SMC binary galaxy and stripped H Ⅰ gas from the Clouds to form the Magellanic Stream. We adopt two general prescriptions for the Galactic potential and construct the past orbital history of several segments of the Stream. We show that the discrepancy between the observational data and previous theoretical predictions can be reconciled if, and only if, the Galactic halo has a mass ～5.5 ± 1 x 10~(11) solar mass within 100 kpc and a substantial fraction (～ 1/2) of this mass is distributed beyond the present Galactic distance of the Magellanic Clouds ( ≥ 50 kpc). This mass is nearly half that assumed in the previous models, but it is consistent with some recent estimates for the Galactic halo. Beyond 100 kpc this mass may continue to increase to ～10~(12) solar mass within its tidal radius (～300 kpc). However, the modification of the Galactic potential does not lead to any major alteration in the dynamical evolution of the Magellanic Clouds. Similar to previous theoretical results, our analyses show that (1) the Magellanic Clouds are near perigalacticon, (2) they are gravitationally bound to the Galaxy with apogalacticon beyond 100 kpc, (3) the SMC and LMC are binary galaxies and will become separated in the next 1-2 Gyr, (4) the Clouds possess a total angular momentum comparable to that of Population I stars in the Galactic disk, (5) gas in the Stream is likely to have originated from the SMC between 1-2 Gyr ago; and (6) the mass in the Stream is comparable to the gas content in the SMC. Finally, we predict both the distance and proper motion of the gas and stars along the Stream, which may be measured to verify the validity of the theoretical model. We also predict the Galactocentric transverse velocity of the SMC to be 200 ± 100 km s~(-1).
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机译：最近的正常运动观测表明麦哲伦星云正在引领麦哲伦星系流。尽管该运动的方向与有关云的动力学和流的起源的理论模型所期望的方向一致，但其幅度远小于预测的幅度。我们重新审视了最初的推测，即过去14 x 10〜9年中，银河以潮汐的方式破坏了LMC-SMC二元星系，并从云中剥离了HⅠ气体以形成麦哲伦流。对于银河系潜力，我们采用了两种一般性的处方，并构造了溪流几段的过去轨道历史。我们表明，当且仅当银河系晕的质量在100 kpc内质量为〜5.5±1 x 10〜（11）太阳质量且很大一部分（〜1）时，观测数据与先前的理论预测之间的差异才可以调和。该质量的/ 2）超出了麦哲伦星云当前的银河距离（≥50 kpc）。该质量几乎是先前模型中假定的质量的一半，但与最近对银河晕的一些估计相一致。超过100 kpc时，该质量可能会在其潮汐半径（〜300 kpc）内继续增加到约10〜（12）太阳质量。但是，对银河系潜力的修改不会导致麦哲伦星云的动力学演化发生任何重大变化。与以前的理论结果相似，我们的分析表明：（1）麦哲伦星云靠近银河系;（2）重力银团以超过100 kpc的远距银团与银河系结合;（3）SMC和LMC是双星系，将分离在接下来的1-2 Gyr中，（4）云层的总角动量与银河系盘中的I类恒星相当，（5）溪流中的气体很可能起源于1-2 Gyr之间的SMC前; （6）流中的质量与SMC中的气体含量相当。最后，我们预测了气体和恒星沿流的距离和适当的运动，可以对其进行测量以验证理论模型的有效性。我们还预测SMC的半圆心横向速度为200±100 km s〜（-1）。
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