无凸起星系的分级形成：为什么流出物具有低angular momentum
Hierarchical formation of bulgeless galaxies: Why outflows have low angular momentum
摘要：
使用高分辨率，完全宇宙学平滑粒子流体动力学模拟的矮星系在λ冷暗物质宇宙中，我们展示了重子如何达到最终的角动量分布，使纯盘星系的形成。通过超新星和恒星风吹出大量的气体，这在观测上得到了很好的支持，是形成无凸起圆盘的关键因素。我们概述了为什么星系外流优先删除低角动量的材料，并表明这是一个自然的结果时，结构形成在一个冷的暗物质宇宙学。驱动因素是：a）吸积物质的平均角动量随时间增加，b）早期较低的电势，c）存在一个扩展的高角动量气体储层，该储层不在恒星形成区域内，这意味着只有来自内部区域的气体（低角动量气体）被排出，以及d）流出物遵循垂直于盘的阻力最小的路径的趋势。我们还表明，外流增强合并过程中，从而驱逐了大部分的气体已经失去了角动量，在这些事件中，并防止形成“经典”，合并驱动的低质量系统的凸起。在这种合并之前形成的恒星形成了一个弥散的、扩展的恒星晕成分。
英文摘要：
Using high resolution, fully cosmological smoothed particle hydro-dynamical simulations of dwarf galaxies in a Lambda cold dark matter Universe, we show how baryons attain a final angular momentum distribution which allows pure disc galaxies to form. Blowing out substantial amounts of gas through supernovae and stellar winds, which is well supported observationally, is a key ingredient in forming bulgeless discs. We outline why galactic outflows preferentially remove low angular momentum material, and show that this is a natural result when structure forms in a cold dark matter cosmology. The driving factors are a) the mean angular momentum of accreted material increases with time, b) lower potentials at early times, c) the existence of an extended reservoir of high angular momentum gas which is not within star forming regions, meaning that only gas from the inner region (low angular momentum gas) is expelled and d) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of "classical", merger driven bulges in low mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component.
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