最微弱Milky Way卫星的潮汐特征：狮子座五号、双鱼座II和犬座维纳星II的详细性质
Tidal Signatures in the Faintest Milky Way Satellites: The Detailed Properties of Leo V, Pisces II and Canes Venatici II
摘要：
我们提出了三个最近发现的暗淡的银河系卫星：狮子座V，双鱼座II，和犬Venaeros II的深宽视场测光。我们的主要目标是研究这些矮星的结构和恒星形成历史，我们也在寻找潮汐扰动的迹象。这三颗卫星的半光半径（$\sim 60-90$ pc）相似，但椭圆度范围很广。Leo V和CVn II都显示出在大半径处有类似流的高密度迹象。对卫星颜色-星等图的分析表明，这三个天体都很老（$>$ 10 Gyr），而且金属含量很低（[Fe/H] $\sim -2$），不过模型和数据都没有足够的精确度来评估卫星是何时在宇宙再电离作用下形成的。缺乏观测到的年轻恒星群（$\la 10$ Gyr）可能使它们与银河系中心距离为$\ga 150$ kpc的其他卫星分开。我们提出了一个新的编译的结构数据的所有银河系卫星星系，并使用它来比较经典的超微弱的矮星的属性。在$\sim$ 2- $σ$水平上，两组的椭圆率分布是一致的。然而，最暗的卫星往往更倾向于向银河系中心排列，而那些椭圆率最高的卫星（$\ga 0.4$）的方位（$Δθ_{GC}$）在$20^{\circ} \lesssim Δθ_{GC} \lesssim 40^{\circ}$范围内。后一种观测结果与矮星系模拟的预测大致一致，矮星系已经失去了相当大一部分暗物质晕，并且正在被潮汐剥离。
英文摘要：
We present deep wide-field photometry of three recently discovered faint Milky Way satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals are to study the structure and star formation history of these dwarfs; we also search for signs of tidal disturbance. The three satellites have similar half-light radii ($\sim 60-90$ pc) but a wide range of ellipticities. Both Leo V and CVn II show hints of stream-like overdensities at large radii. An analysis of the satellite color-magnitude diagrams shows that all three objects are old ($>$ 10 Gyr) and metal-poor ([Fe/H] $\sim -2$), though neither the models nor the data have sufficient precision to assess when the satellites formed with respect to cosmic reionization. The lack of an observed younger stellar population ($\la 10$ Gyr) possibly sets them apart from the other satellites at Galactocentric distances $\ga 150$ kpc. We present a new compilation of structural data for all Milky Way satellite galaxies and use it to compare the properties of classical dwarfs to the ultra-faints. The ellipticity distribution of the two groups is consistent at the $\sim$2-$σ$ level. However, the faintest satellites tend to be more aligned toward the Galactic center, and those satellites with the highest ellipticity ($\ga 0.4$) have orientations ($Δθ_{GC}$) in the range $20^{\circ} \lesssim Δθ_{GC} \lesssim 40^{\circ}$. This latter observation is in rough agreement with predictions from simulations of dwarf galaxies that have lost a significant fraction of their dark matter halos and are being tidally stripped.
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