标题： 大麦哲伦星云中被吸积的SMC恒星群体 显示英文标题

标题： A Population of Accreted SMC Stars in the LMC

摘要： 我们基于约5900个新的和现有的大质量红超巨星、富氧和富碳的AGB星以及其他巨星的速度，分析了大麦云的恒星运动学。在对LMC的空间运动进行修正并考虑AGB星族的不对称漂移后，我们得出的旋转曲线与所有使用的示踪物以及已发表的HI数据一致。旋转曲线的幅度在半径R_0=2.4+/-0.1 kpc以外为v_0=87+/-5 km s^-1，并且运动学节点线的位置角为theta=142度+/-5度。通过检查我们的拟合中的异常值，我们识别出一个376颗恒星的群体，或超过~5%的样本，它们的视线速度似乎与LMC盘的旋转方向相反。我们发现这些运动学上不同的恒星要么在与LMC盘紧密对齐的平面上逆向旋转，要么以与LMC盘相同的方向旋转，但其平面相对于LMC倾斜54度+/-2度。它们的运动学清楚地将它们与两个已知的HI臂联系起来，这些臂以前被解释为从LMC中拉出的。我们测量了约1000颗LMC场星和30颗运动学上不同的恒星的Ca三重线金属量。对于LMC场星，我们发现中位数[Fe/H]=-0.56 +/- 0.02，离散度为0.5 dex，而对于运动学上不同的恒星，中位数[Fe/H]为-1.25 +/- 0.13，离散度为0.7 dex。金属量差异提供了强有力的证据，表明运动学上不同的恒星起源于SMC。这种解释意味着与恒星运动学相关的HI臂可能正在落入LMC，而不是被拉出。 显示英文摘要

摘要： We present an analysis of the stellar kinematics of the Large Magellanic Cloud based on ~5900 new and existing velocities of massive red supergiants, oxygen-rich and carbon-rich AGB stars, and other giants. After correcting the line-of-sight velocities for the LMC's space motion and accounting for asymmetric drift in the AGB population, we derive a rotation curve that is consistent with all of the tracers used, as well as that of published HI data. The amplitude of the rotation curve is v_0=87+/-5 km s^-1 beyond a radius R_0=2.4+/-0.1 kpc, and has a position angle of the kinematic line of nodes of theta=142 degrees +/-5 degrees. By examining the outliers from our fits, we identify a population of 376 stars, or >~5% of our sample, that have line-of-sight velocities that apparently oppose the sense of rotation of the LMC disk. We find that these kinematically distinct stars are either counter-rotating in a plane closely aligned with the LMC disk, or rotating in the same sense as the LMC disk, but in a plane that is inclined by 54 degrees +/- 2 degrees to the LMC. Their kinematics clearly link them to two known HI arms, which have previously been interpreted as being pulled out from the LMC. We measure metallicities from the Ca triplet lines of ~1000 LMC field stars and 30 stars in the kinematically distinct population. For the LMC field, we find a median [Fe/H]=-0.56 +/- 0.02 with dispersion of 0.5 dex, while for the kinematically distinct stars the median [Fe/H] is -1.25 +/- 0.13 with a dispersion of 0.7 dex. The metallicity differences provide strong evidence that the kinematically distinct population originated in the SMC. This interpretation has the consequence that the HI arms kinematically associated with the stars are likely falling into the LMC, instead of being pulled out.