Dynamics of the Magellanic Clouds in a Lambda cold dark matter universe
Dynamics of the Magellanic Clouds in a Lambda cold dark matter universe
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Lambda 冷暗物质宇宙中麦哲伦星云的动力学
DOI：
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发表时间：
2018
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通讯作者：
L. Hernquist
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作者：
M. Boylan;G. Besla;L. Hernquist
我们研究了从千年二号模拟中选择的银河系-麦哲伦云系统，以便将麦哲伦云的轨道置于宇宙学背景下。我们的分析表明，质量足以与 LMC 类似的卫星通常是在后期吸积的。此外，那些在早期吸积并存活至今的轨道特性与大麦哲伦观测到的轨道特性不一致。 LMC 的高速度，加上模拟中缺乏自由轨道，表明 MW 光环的质量不太可能小于 2 × 10 12 M (cid:12)。这一结论得到了卫星晕的统计数据的进一步支持，这些卫星的质量、速度和间隔与大麦哲伦的卫星相当。我们进一步表明：（1）LMC 和 SMC 质量天体在 MW 质量晕中并不少见； (2) LMC 明显较高的角动量在宇宙学上并不罕见； (3) MW 晕在 z = 0 处托管 LMC-SMC 双星系统的情况很少见，但后期积累的高速双星对是可能的。根据这些结果，我们得出结论，LMC 在过去 4 Gyr 内吸积，目前正在围绕 MW 进行首次中心周穿越。
We examine Milky Way-Magellanic Cloud systems selected from the Millennium-II Simulation in order to place the orbits of the Magellanic Clouds in a cosmological context. Our analysis shows that satellites massive enough to be LMC analogs are typically accreted at late times. Moreover, those that are accreted at early times and survive to the present have orbital properties that are discrepant with those observed for the LMC. The high velocity of the LMC, coupled with the dearth of unbound orbits seen in the simulation, argues that the mass of the MW’s halo is unlikely to be less than 2 × 10 12 M (cid:12) . This conclusion is further supported by statistics of halos hosting satellites with masses, velocities, and separations comparable to those of the LMC. We further show that: (1) LMC and SMC-mass objects are not particularly uncommon in MW-mass halos; (2) the apparently high angular momentum of the LMC is not cosmologically unusual; and (3) it is rare for a MW halo to host a LMC-SMC binary system at z = 0, but high speed binary pairs accreted at late times are possible. Based on these results, we conclude that the LMC was accreted within the past four Gyr and is currently making its first pericentric passage about the MW.