飞马座-双鱼座拱中速云的长尾
The Long Tails of the Pegasus-Pisces Arch Intermediate Velocity Cloud
摘要：
我们目前的飞马座双鱼座（PP拱），在我们的银河系中的中速云的流体动力学模拟。PP Arch，也被称为IVC 86 - 36，在中等和高速云中是独一无二的，因为它的双尾非常长和窄。它的视线速度约为50公里/秒，符合中速云的标准，但尾部的方向表明，云的总三维速度至少为100公里/秒。这个速度是超音速的在赫氏层和厚盘。我们模拟了云，因为它通过银河系厚和薄磁盘在一个倾斜的角度相对于中平面超音速旅行。我们模拟的云长出了长长的双尾，合理地再现了PP拱头部的H I 21~cm强度和速度。弓形激波保护了每个模拟云免受过度剪切，并降低了其雷诺数。这些因素同样可以保护PP Arch，并使其异常长的尾巴得以生存。模拟预测了未来云的流体动力学行为，当它与更接近银河系中平面的密度更大的气体碰撞时。看来PP拱的命运是变形，消散，并与银河系盘合并。
英文摘要：
We present hydrodynamic simulations of the Pegasus-Pisces (PP Arch), an intermediate velocity cloud in our Galaxy. The PP Arch, also known as IVC 86-36, is unique among intermediate and high velocity clouds, because its twin tails are unusually long and narrow. Its -50 km/s line-of-sight velocity qualifies it as an intermediate velocity cloud, but the tails' orientations indicate that the cloud's total three-dimensional speed is at least ~100 km/s. This speed is supersonic in the Reynold's Layer and thick disk. We simulated the cloud as it travels supersonically through the Galactic thick and thin disks at an oblique angle relative to the midplane. Our simulated clouds grow long double tails and reasonably reproduce the H I 21~cm intensity and velocity of the head of the PP Arch. A bow shock protects each simulated cloud from excessive shear and lowers its Reynolds number. These factors may similarly protect the PP Arch and enable the survival of its unusually long tails. The simulations predict the future hydrodynamic behavior of the cloud when it collides with denser gas nearer to the Galactic midplane. It appears that the PP Arch's fate is to deform, dissipate, and merge with the Galactic disk.
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