The gravitational force field of the Galaxy measured from the kinematics of RR Lyrae in Gaia
The gravitational force field of the Galaxy measured from the kinematics of RR Lyrae in Gaia
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DOI：
10.1093/mnras/stz572
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发表时间：
2018-06
影响因子：
4.8
通讯作者：
C. Wegg;O. Gerhard;M. Bieth
中科院分区：
文献类型：
--
作者：
C. Wegg;O. Gerhard;M. Bieth
从15651 RR天琴座在盖亚DR 2准确自行的样本，我们测量的方位角平均运动的内部恒星晕之间的1.5和20千秒差距的银河系中心。我们发现，他们的运动是强烈的径向各向异性，和他们的速度椭球几乎球形对齐在这个体积。仅在内部区域${\lesssim } 5\，{\rm kpc}\，$中各向异性显著下降（但仍具有β > 0.25）并且速度椭球向圆柱形排列倾斜。在内部区域，我们的晕星样本的旋转速度高达50\，{\rm km}\，{\rm s}^{-1}\，$，这可能反映了银河系的早期历史，尽管在这些半径处与银河系棒也有显著的角动量交换。随后，我们应用Jeans方程这些运动学测量，以非参数化地推断在这个体积上的方位平均引力加速度场，并通过去除重子物质的贡献，测量暗物质的贡献。我们发现暗物质的引力势近似为球形，平均扁平度在5 ~ 20 kpc之间，通过拟合参数椭球密度分布，我们测量到暗物质晕在这些半径上的扁平度为q\rho ={1.00 \pm 0.09\，}\！$
From a sample of 15651 RR Lyrae with accurate proper motions in Gaia DR2, we measure the azimuthally averaged kinematics of the inner stellar halo between 1.5 and 20 kpc from the Galactic centre. We find that their kinematics are strongly radially anisotropic, and their velocity ellipsoid nearly spherically aligned over this volume. Only in the inner regions ${\lesssim } 5\, {\rm kpc}\,$ does the anisotropy significantly fall (but still with β > 0.25) and the velocity ellipsoid tilt towards cylindrical alignment. In the inner regions, our sample of halo stars rotates at up to $50\, {\rm km}\, {\rm s}^{-1}\,$, which may reflect the early history of the Milky Way, although there is also a significant angular momentum exchange with the Galactic bar at these radii. We subsequently apply the Jeans equations to these kinematic measurements in order to non-parametrically infer the azimuthally averaged gravitational acceleration field over this volume, and by removing the contribution from baryonic matter, measure the contribution from dark matter. We find that the gravitational potential of the dark matter is nearly spherical with average flattening $q_\Phi ={1.01 \pm 0.06\, }$ between 5 and 20 kpc, and by fitting parametric ellipsoidal density profiles to the acceleration field, we measure the flattening of the dark matter halo over these radii to be $q_\rho ={1.00 \pm 0.09\, }\!.$