绕Andromeda Galaxy运行的同向旋转矮星系的巨大薄平面
A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
摘要：
矮卫星星系被认为是原始结构人口的残余物，这些原始结构合并形成了像银河系这样的巨大星系。早期的分析指出，矮星系可能不是各向同性地分布在我们的银河系周围，因为有几个矮星系与HI发射流相关，并且可能形成共面的星系群。这些怀疑得到了最近分析的支持，有人声称，卫星表面上的平面分布在标准宇宙学中是无法预测的，不能简单地代表过去相干吸积的记忆。然而，其他研究对这一结论提出了质疑。在这里，我们报告的存在（99.998%的显着性）的一个平面子群的卫星在仙女座星系，包括约50%的人口。该结构非常巨大：直径至少为400 kpc，但也非常薄，垂直散射<14.1 kpc（99%置信度）。径向速度测量表明，在这个结构中的卫星有相同的旋转方向围绕他们的主机。这一发现最终表明，大量的矮卫星星系共享相同的动力学轨道特性和角动量的方向，为我们理解这些最暗物质占主导地位的星系的起源提供了新的见解。有趣的是，我们确定的平面大致与银河系圆盘的极点对齐，并且与银河系到仙女座的位置矢量共面。在大质量星系晕中存在如此广泛的相干运动学结构是一个必须在星系形成和宇宙学框架内解释的事实。
英文摘要：
Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. An early analysis noted that dwarf galaxies may not be isotropically distributed around our Galaxy, as several are correlated with streams of HI emission, and possibly form co-planar groups. These suspicions are supported by recent analyses, and it has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. However, other studies dispute this conclusion. Here we report the existence (99.998% significance) of a planar sub-group of satellites in the Andromeda galaxy, comprising approximately 50% of the population. The structure is vast: at least 400 kpc in diameter, but also extremely thin, with a perpendicular scatter <14.1 kpc (99% confidence). Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This finding shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum, a new insight for our understanding of the origin of these most dark matter dominated of galaxies. Intriguingly, the plane we identify is approximately aligned with the pole of the Milky Way's disk and is co-planar with the Milky Way to Andromeda position vector. The existence of such extensive coherent kinematic structures within the halos of massive galaxies is a fact that must be explained within the framework of galaxy formation and cosmology.
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