分子云turbulence是由外部超新星爆炸驱动的吗？
Is molecular cloud turbulence driven by external supernova explosions?
摘要：
我们提出了高分辨率（$\sim$ 0.1 pc），流体动力学和磁流体动力学模拟调查是否可以产生和维持外部超新星（SN）爆炸所观察到的分子云（MC）湍流水平。MC是在大尺度银河系环境中自洽形成的，其形成过程是H $_2$和CO的非平衡形成过程，包括（自）屏蔽和重要的加热和冷却过程。MC从扩散ISM中继承了其初始湍流水平，其中湍流由SN爆炸注入。然而，通过系统地探索个别SNe离开云外的影响，我们发现，在后期阶段，SN驱动湍流的重要性显着降低。这适用于不同的MC质量以及具有和不具有磁场的MC。SN的影响也随着距离的增大而迅速减小。附近的SNe（$d$ $\sim$ 25 pc）将MC的湍流速度分散提高了70%（高达几km s $^{-1}$）。然而，对于$d$ $>$ 50 pc，它们的影响随着$d$的增加而快速降低，几乎可以忽略不计。对于所有探测的距离，速度色散的增益在几十万年内迅速衰减。这明显短于在太阳邻域条件下（$\sim$ 200万年）MC被附近SN撞击的平均时间尺度。因此，在这些条件下，SNe不能维持所观察到的MC湍流水平。然而，在具有高气体表面密度和SN率的环境中，如中央分子区，观察到的升高的MC分散可以由外部SNe触发。
英文摘要：
We present high-resolution ($\sim$ 0.1 pc), hydrodynamical and magnetohydrodynamical simulations to investigate whether the observed level of molecular cloud (MC) turbulence can be generated and maintained by external supernova (SN) explosions. The MCs are formed self-consistently within their large-scale galactic environment following the non-equilibrium formation of H$_2$ and CO including (self-) shielding and important heating and cooling processes. The MCs inherit their initial level of turbulence from the diffuse ISM, where turbulence is injected by SN explosions. However, by systematically exploring the effect of individual SNe going off outside the clouds, we show that at later stages the importance of SN driven turbulence is decreased significantly. This holds for different MC masses as well as MCs with and without magnetic fields. The SN impact also decreases rapidly with larger distances. Nearby SNe ($d$ $\sim$ 25 pc) boost the turbulent velocity dispersions of the MC by up to 70 per cent (up to a few km s$^{-1}$). For $d$ $>$ 50 pc, however, their impact decreases fast with increasing $d$ and is almost negligible. For all probed distances the gain in velocity dispersion decays rapidly within a few 100 kyr. This is significantly shorter than the average timescale for a MC to be hit by a nearby SN under solar neighbourhood conditions ($\sim$ 2 Myr). Hence, at these conditions SNe are not able to sustain the observed level of MC turbulence. However, in environments with high gas surface densities and SN rates like the Central Molecular Zone, observed elevated MC dispersions could be triggered by external SNe.
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