Gaia Proper Motions and Orbits of the Ultra-faint Milky Way Satellites
Gaia Proper Motions and Orbits of the Ultra-faint Milky Way Satellites
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DOI：
10.3847/1538-4357/aacdfb
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发表时间：
2018-04
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影响因子：
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通讯作者：
J. Simon
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文献类型：
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作者：
J. Simon
盖亚使命（DR 2）发布的第二个数据提供了一个全面的和前所未有的图片，在天空平面上的天文源的运动，从太阳附近延伸到银河系的外部。我提出自行测量的基础上盖亚DR 2的17个超微弱的矮星系在100千秒差距的银河系。我从文献中收集了每个矮星中光谱确认的成员星，这些成员星足够明亮，可以进行盖亚天体测量，产生的成员样本从三角座II的两颗恒星到牧夫座I的68颗恒星不等。从分光成员星表，我估计每个系统的自行。我发现与盖亚合作组导出的牧夫座I和狮子座I的自行很好地吻合。17个矮星中有14个的切向速度被确定为优于50 km s-1，比银河系卫星星系的此类测量样本增加了一倍多。轨道近心点受到很好的约束，平均值为38千秒差距。只有一颗卫星Tucana III在银河系中心15 kpc的轨道上，这表明剩下的超暗矮星不太可能经历过严重的潮汐剥离。作为一个群体，超暗矮星处于高速，偏心，逆行的轨道上，几乎所有的空间运动都超过370 km s-1。绝大多数物体目前都接近其轨道的近心点。在低质量（Mvir = 0.9 × 1012 M）的银河系势中，17个星系中有8个缺乏定义明确的远心，似乎是第一次坠落，这表明银河系的质量可能比以前估计的要大，或者许多超暗矮星与麦哲伦云有关。超暗矮轨道的中位离心率为0.79，与数值模拟中看到的值相似，但与更明亮的矮椭球体的圆形轨道不同。
The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar neighborhood to the outer reaches of the Milky Way. I present proper-motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100 kpc of the Milky Way. I compile the spectroscopically confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from two stars in Triangulum II to 68 stars in Boötes I. From the spectroscopic member catalogs, I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Boötes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50 km s−1, more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well constrained, with a mean value of 38 kpc. Only one satellite, Tucana III, is on an orbit passing within 15 kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on high-velocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370 km s−1. A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (Mvir = 0.9 × 1012 M⊙) Milky Way potential, eight out of the 17 galaxies lack well-defined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations but distinct from the rounder orbits of the more luminous dwarf spheroidals.