吸积并不驱动银河系中的Turbulence
Accretion Does Not Drive the Turbulence in Galactic Disks
摘要：
冷气体的快速吸积在气体进入星系中起着至关重要的作用。有人认为，这种吸积沿着狭窄的气流进行，也可能直接驱动星系气体的湍流，动力学扰动和隆起的形成。然而，在宇宙学模拟中，不可能将吸积效应与内部不稳定性和合并分离开来。此外，在大多数宇宙学模拟中，由恒星反馈引起的ISM中的相结构和湍流被以亚网格方式处理，因此反馈不能产生ISM湍流。因此，在本文中，我们测试冷流的影响，否则孤立的星系盘使用详细的模型恒星形成和反馈的极高分辨率的模拟，然后我们包括或排除模拟冷流落在星系的吸积率，速度和几何设置，以最大限度地提高其对磁盘的影响。我们发现：（1）无论有无冷流，气体圆盘中的湍流速度弥散都是相同的;由冷流注入的能量在与圆盘相遇的地方耗散掉。(2)在没有恒星反馈的运行中，冷流的存在对失控的局部坍缩基本上没有影响，导致恒星形成率（SFR）太大。(3)带反馈的冷流运行，冷流具有更高的SFR，但仅在它们具有更多气体的情况下。(4)由于流动相对于盘是延伸的，它们不会触发强共振响应，因此引起弱形态扰动（通过不稳定性的凸起形成不会加速）。(5)然而，流动可以通过面外流的直接贡献来破坏盘。我们的结论是，虽然流入是至关重要的宇宙学时间尺度，以确定供应和角动量的气体盘，它们对星系的瞬时动力学效应弱。
英文摘要：
Rapid accretion of cold gas plays a crucial role in getting gas into galaxies. It has been suggested that this accretion proceeds along narrow streams that might also directly drive the turbulence in galactic gas, dynamical disturbances, and bulge formation. In cosmological simulations, however, it is impossible to isolate and hence disentangle the effect of accretion from internal instabilities and mergers. Moreover, in most cosmological simulations, the phase structure and turbulence in the ISM arising from stellar feedback are treated in a sub-grid manner, so that feedback cannot generate ISM turbulence. In this paper we therefore test the effects of cold streams in extremely high-resolution simulations of otherwise isolated galaxy disks using detailed models for star formation and feedback; we then include or exclude mock cold flows falling onto the galaxies with accretion rates, velocities and geometry set to maximize their effect on the disk. We find: (1) Turbulent velocity dispersions in gas disks are identical with or without the cold flow; the energy injected by the flow is dissipated where it meets the disk. (2) In runs without stellar feedback, the presence of a cold flow has essentially no effect on runaway local collapse, resulting in star formation rates (SFRs) that are far too large. (3) Disks in runs with feedback and cold flows have higher SFRs, but only insofar as they have more gas. (4) Because flows are extended relative to the disk, they do not trigger strong resonant responses and so induce weak morphological perturbation (bulge formation via instabilities is not accelerated). (5) However, flows can thicken the disk by direct contribution of out-of-plane streams. We conclude that while inflows are critical over cosmological timescales to determine the supply and angular momentum of gas disks, they have weak instantaneous dynamical effects on galaxies.
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