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Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC ? ??

机译： Gaia DR 2和VLT / FLAMES搜索LMC的新卫星？ ??

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A wealth of tiny galactic systems populates the surroundings of the Milky Way. However, some of these objects might have originated as former satellites of the Magellanic Clouds, in particular of the Large Magellanic Cloud (LMC). Examples of the importance of understanding how many systems are genuine satellites of the Milky Way or the LMC are the implications that the number and luminosity-mass function of satellites around hosts of different mass have for dark matter theories and the treatment of baryonic physics in simulations of structure formation. Here we aim at deriving the bulk motions and estimates of the internal velocity dispersion and metallicity properties in four recently discovered distant southern dwarf galaxy candidates, Columba I, Reticulum III, Phoenix II, and Horologium II. We combined Gaia DR2 astrometric measurements, photometry, and new FLAMES/GIRAFFE intermediate-resolution spectroscopic data in the region of the near-IR Ca II triplet lines; this combination is essential for finding potential member stars in these low-luminosity systems. We find very likely member stars in all four satellites and are able to determine (or place limits on) the bulk motions and average internal properties of the systems. The systems are found to be very metal poor, in agreement with dwarf galaxies and dwarf galaxy candidates of similar luminosity. Of these four objects, we can only firmly place Phoenix II in the category of dwarf galaxies because of its resolved high velocity dispersion (9.5_(?4.4)~(+6.8)km s~(?1)) and intrinsic metallicity spread (0.33 dex). For Columba I we also measure a clear metallicity spread. The orbital pole of Phoenix II is well constrained and close to that of the LMC, suggesting a prior association. The uncertainty on the orbital poles of the other systems is currently very large, so that an association cannot be excluded, except for Columba I. Using the numbers of potential former satellites of the LMC identified here and in the literature, we obtain for the LMC a dark matter mass of M _(200)= 1.9_(?0.9)~(+1.3)× 10~(11) M _(⊙).
机译：银河系周围遍布着许多微小的银河系。但是，其中一些物体可能起源于麦哲伦星云的早期卫星，特别是大麦哲伦星云（LMC）的卫星。理解多少系统是银河系或LMC的真正卫星的重要性的例子是不同质量宿主周围的卫星的数量和光度-质量功能对暗物质理论和模拟中重子物理学的影响结构的形成。在这里，我们的目的是推导最近发现的四个遥远的南方矮星系候选者，哥伦巴一号，网状三号，凤凰二号和天文馆二号的整体运动以及内部速度色散和金属性的估计。我们将Gaia DR2天文测量，光度学和近红外Ca II三重态谱线区域中的新FLAMES / GIRAFFE中分辨率光谱数据结合在一起;这种组合对于在这些低发光度系统中寻找潜在的恒星至关重要。我们在所有四颗卫星中都非常可能发现成员恒星，并且能够确定（或限制）系统的整体运动和平均内部属性。发现该系统非常贫金属，与矮度星系和类似光度的矮度星系候选者一致。在这四个天体中，我们只能将Phoenix II牢牢地定位在矮星系的类别中，这是因为它解析出了高速色散（9.5 _（？4.4）〜（+6.8）km s〜（？1））和固有的金属性扩散（ 0.33 dex）。对于Columba I，我们还测量了明显的金属分布。 “凤凰二号”的轨道极受到约束，并且与LMC的轨道极接近，这暗示了先前的联系。当前，其他系统的轨道极点的不确定性非常大，因此，除了哥伦巴I号外，无法排除一个关联。使用这里和文献中确定的LMC的潜在前卫星的数量，我们可以获得LMC暗物质质量为M _（200）= 1.9 _（？0.9）〜（+1.3）×10〜（11）M _（⊙）。

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