Velocity anti - correlation of diametrically opposed galaxy satellites in the low-redshift Universe

摘要

银河系和仙女座这两个星系都与明显在同一平面内一起转动的若干矮卫星星系相关。这篇论文表明,卫星星系的这种一起转动的平面也许是普遍性的。Rodrigo Ibata及同事测量了本宇宙中成对的截然相反的卫星星系的速度,发现在相距150千秒差距时它们倾向于反关联（anti-correlated);在更大尺度的、相距大约2兆秒差距的环境中,星系主要沿连接"内卫星星系对"(inner satellite pair)的轴心成团分布。%Recent work has shown that the Milky Way and the Andromeda galaxies both possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is interesting to evaluate the incidence of such planar structures in the larger galactic population, because the Local Group may not be a representative environment. Here we report measurements of the velocities of pairs of diametrically opposed satellite galaxies. In the local Universe (redshift z ＜ 0.05), we find that satellite pairs out to a distance of 150 kiloparsecs from the galactic centre are preferentially anti-correlated in their velocities (99.994 per cent confidence level), and that the distribution of galaxies in the larger-scale environment (out to distances of about 2 megaparsecs) is strongly clumped along the axis joining the inner satellite pair (＞7σconfidence). This may indicate that planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous, and their coherent motion suggests that they represent a substantial repository of angular momentum on scales of about 100 kiloparsecs.