The Recent LMC–SMC Collision: Timing and Impact Parameter Constraints from Comparison of Gaia LMC Disk Kinematics and N-body Simulations
The Recent LMC–SMC Collision: Timing and Impact Parameter Constraints from Comparison of Gaia LMC Disk Kinematics and N-body Simulations
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DOI：
10.3847/1538-4357/ac4e90
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发表时间：
2022-01
期刊：
影响因子：
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通讯作者：
Yumi Choi;K. Olsen;G. Besla;R. P. van der Marel;P. Zivick;N. Kallivayalil;D. Nidever
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文献类型：
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作者：
Yumi Choi;K. Olsen;G. Besla;R. P. van der Marel;P. Zivick;N. Kallivayalil;D. Nidever
我们目前的自行（PM）在大麦哲伦云（LMC）磁盘使用盖亚早期数据发布3目录的红色团块星的分析。使用一个运动学模型的基础上的老恒星的三维速度测量，我们构建了剩余PM场减去质心运动和内部旋转运动分量。残留PM领域揭示了不对称的模式，包括较大的残留PM在南部磁盘。所观察到的剩余PM场与五个数值模拟的LMC模拟，是受银河系和小麦哲伦云（SMC）的潮汐场的比较表明，目前的LMC是不处于动态平衡。我们发现观测到的盘加热水平（PM残差均方根为0.057 ± 0.002质量/年）和运动学不对称性都不能被银河系潮汐或SMC撞击参数大于LMC盘的大小所再现。这种测量的磁盘加热水平提供了一种新的和重要的方法来验证数值模拟的LMC-SMC相互作用的历史。仅我们的研究结果就限制了撞击参数<10 kpc和撞击时间<2.5亿年。当采用从以前的研究中获得的1.4亿至1.6亿年前的撞击时间限制时，我们的结果表明，最近的SMC遭遇一定是在撞击参数为1.5千秒差距时发生的。我们还发现一致的径向趋势的运动学和几何推导磁盘倾角和线的节点位置角，表明一个共同的起源。
We present analysis of the proper-motion (PM) field of the red clump stars in the Large Magellanic Cloud (LMC) disk using the Gaia Early Data Release 3 catalog. Using a kinematic model based on old stars with 3D velocity measurements, we construct the residual PM field by subtracting the center-of-mass motion and internal rotation motion components. The residual PM field reveals asymmetric patterns, including larger residual PMs in the southern disk. Comparisons of the observed residual PM field with those of five numerical simulations of an LMC analog that is subject to the tidal fields of the Milky Way and the Small Magellanic Cloud (SMC) show that the present-day LMC is not in dynamical equilibrium. We find that both the observed level of disk heating (PM residual rms of 0.057 ± 0.002 mas yr−1) and kinematic asymmetry are not reproduced by Milky Way tides or if the SMC impact parameter is larger than the size of the LMC disk. This measured level of disk heating provides a novel and important method to validate numerical simulations of the LMC–SMC interaction history. Our results alone put constraints on an impact parameter ≲10 kpc and impact timing <250 Myr. When adopting the impact timing constraint of ∼140–160 Myr ago from previous studies, our results suggest that the most recent SMC encounter must have occurred with an impact parameter of ∼5 kpc. We also find consistent radial trends in the kinematically and geometrically derived disk inclination and line-of-node position angles, indicating a common origin.