Mayer L, Kazantzidis S, Mastropietro C, Wadsley J
Institute for Theoretical Physics, University of Zurich, Winterthurestrasse 190, CH-8057 Zürich, Switzerland.
Nature. 2007 Feb 15;445(7129):738-40. doi: 10.1038/nature05552.
The known galaxies most dominated by dark matter (Draco, Ursa Minor and Andromeda IX) are satellites of the Milky Way and the Andromeda galaxies. They are members of a class of faint galaxies, devoid of gas, known as dwarf spheroidals, and have by far the highest ratio of dark to luminous matter. None of the models proposed to unravel their origin can simultaneously explain their exceptional dark matter content and their proximity to a much larger galaxy. Here we report simulations showing that the progenitors of these galaxies were probably gas-dominated dwarf galaxies that became satellites of a larger galaxy earlier than the other dwarf spheroidals. We find that a combination of tidal shocks and ram pressure swept away the entire gas content of such progenitors about ten billion years ago because heating by the cosmic ultraviolet background kept the gas loosely bound: a tiny stellar component embedded in a relatively massive dark halo survived until today. All luminous galaxies should be surrounded by a few extremely dark-matter-dominated dwarf spheroidal satellites, and these should have the shortest orbital periods among dwarf spheroidals because they were accreted early.
已知受暗物质主导程度最高的星系（天龙座星系、小熊座星系和仙女座IX星系）是银河系和仙女座星系的卫星。它们属于一类微弱的、没有气体的星系，被称为矮球状星系，并且具有迄今为止最高的暗物质与发光物质比例。为解释其起源而提出的所有模型，都无法同时解释它们特殊的暗物质含量以及它们与一个大得多的星系的接近程度。在此，我们报告的模拟结果表明，这些星系的前身可能是以气体为主的矮星系，它们比其他矮球状星系更早成为一个更大星系的卫星。我们发现，大约在100亿年前，潮汐冲击和冲压压力的共同作用扫除了这些前身星系的全部气体，这是因为宇宙紫外线背景的加热使气体保持松散束缚状态：嵌入相对巨大暗物质晕中的微小恒星成分一直存活至今。所有发光星系周围都应该有一些由暗物质极度主导的矮球状卫星，并且由于它们是早期被吸积的，所以这些卫星在矮球状星系中应该具有最短的轨道周期。
