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arXiv 1509.07239astro-ph.GA
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棒星系大设计旋涡的短期动力学演化

Short-term dynamical evolution of grand-design spirals in barred galaxies

Junichi Baba

摘要:

利用三维$N$体/流体动力学模拟研究了棒旋星系中恒星大设计旋臂的短期动力学演化。类似于以前的数值模拟无棒,多臂螺旋,我们发现,在棒星系的宏伟设计的螺旋臂不是静止的,而是动态的。这意味着旋臂的振幅、俯仰角和旋转频率不是恒定的,而是在几亿年内发生变化(即星系的典型旋转周期)。我们还发现,棒星系中清晰的大设计螺旋只有在螺旋与棒的末端连接时才会出现。此外,我们发现,在外部区域($R>$ 1.5- 2杆半径)的螺旋臂的短期行为可以用摆动放大理论来解释,而在内部区域($R<$ 1.5- 2杆半径),杆的影响是不可忽略的。这些结果表明,虽然棒星系中的大设计旋臂受到恒星棒的影响,但大设计旋臂本质上不是起源于棒驱动的固定密度波,而是自激动态模式。我们暗示,即使在棒旋星系中,一个刚性旋转的大设计螺旋也不能成为研究气体流动和云形成的合理动力学模型。

英文摘要:

We investigate the short-term dynamical evolution of stellar grand-design spiral arms in barred spiral galaxies using a three-dimensional (3D) $N$-body/hydrodynamic simulation. Similar to previous numerical simulations of unbarred, multiple-arm spirals, we find that grand-design spiral arms in barred galaxies are not stationary, but rather dynamic. This means that the amplitudes, pitch angles, and rotational frequencies of the spiral arms are not constant, but change within a few hundred million years (i.e. the typical rotational period of a galaxy). We also find that the clear grand-design spirals in barred galaxies appear it only when the spirals connect with the ends of the bar. Furthermore, we find that the short-term behaviour of spiral arms in the outer regions ($R>$ 1.5--2 bar radius) can be explained by the swing amplification theory and that the effects of the bar are not negligible in the inner regions ($R<$ 1.5--2 bar radius). These results suggest that, although grand-design spiral arms in barred galaxies are affected by the stellar bar, the grand-design spiral arms essentially originate not as bar-driven stationary density waves, but rather as self-excited dynamic patterns. We imply that a rigidly rotating grand-design spiral could not be a reasonable dynamical model for investigating gas flows and cloud formation even in barred spiral galaxies.

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