LCDM中的薄、厚和深色椎间盘
Thin, thick and dark discs in LCDM
摘要：
在LCDM宇宙学中，银河系将卫星吸积到恒星盘中。我们使用宇宙学模拟来评估近盘平面和更高倾角吸积事件的频率，以及卫星合并的无碰撞模拟来量化吸积材料的最终状态和对薄盘的影响。平均而言，一个银河系大小的星系有3个Vmax> 80 km/s的暗晕，7个Vmax> 60 km/s的暗晕，15个Vmax> 40 km/s的暗晕在红移z>1处合并。假设是各向同性吸积，其中三分之一会以小于20度的撞击角合并，并被动力摩擦力拖入盘平面。它们的吸积恒星和暗物质形成了一个厚厚的圆盘。恒星厚盘在质量上再现了在太阳附近观测到的厚盘，但质量要小2-10倍。在太阳位置，暗物质盘贡献了0.25-1倍的晕密度。虽然不太可能是动态有趣的，暗盘有重要的意义，直接检测暗物质，因为它的速度相对于地球低。高倾角（>20度）遭遇的可能性是低倾角遭遇的两倍。这些导致了与最近发现的内/外恒星晕非常相似的结构。它们也会对银河系的恒星盘造成更大的破坏，产生更明显的耀斑和翘曲;它们的寿命都很长，而且与目前的观测结果一致。最大质量的合并（vmax> 80 km/s）会将薄盘加热到足以产生厚盘。这些被加热的薄盘星对于获得像银河系那样大质量的厚盘是必不可少的;它们可能包含大约50-90%的厚盘星。银河系薄盘必须在z=1后由新鲜气体重新形成。
英文摘要：
In a LCDM cosmology, the Milky Way accretes satellites into the stellar disc. We use cosmological simulations to assess the frequency of near disc plane and higher inclination accretion events, and collisionless simulations of satellite mergers to quantify the final state of the accreted material and the effect on the thin disc. On average, a Milky Way-sized galaxy has 3 subhalos with vmax>80km/s; 7 with vmax>60km/s; and 15 with vmax>40km/s merge at redshift z>1. Assuming isotropic accretion, a third of these merge at an impact angle <20 degrees and are dragged into the disc plane by dynamical friction. Their accreted stars and dark matter settle into a thick disc. The stellar thick disc qualitatively reproduces the observed thick disc at the solar neighbourhood, but is less massive by a factor ~2-10. The dark matter disc contributes 0.25-1 times the halo density at the solar position. Although not likely to be dynamically interesting, the dark disc has important implications for the direct detection of dark matter because of its low velocity with respect to the Earth. Higher inclination encounters (>20 degrees) are twice as likely as low inclination ones. These lead to structures that closely resemble the recently discovered inner/outer stellar halos. They also do more damage to the Milky Way stellar disc creating a more pronounced flare, and warp; both long-lived and consistent with current observations. The most massive mergers (vmax>80km/s) heat the thin disc enough to produce a thick disc. These heated thin disc stars are essential for obtaining a thick disc as massive as that seen in the Milky Way; they likely comprise some ~50-90% of the thick disc stars. The Milky Way thin disc must reform from fresh gas after z=1 [abridged].
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