Lifetime of a Lopsided Pattern: Damping of Lopsided Disks by Dynamical Friction
Lifetime of a Lopsided Pattern: Damping of Lopsided Disks by Dynamical Friction
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不平衡模式的寿命：动态摩擦对不平衡盘的阻尼
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发表时间：
2002
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通讯作者：
Makoto Ideta
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作者：
Makoto Ideta
使用线性微扰理论研究了动摩擦对不平衡圆盘时间演化的影响。摩擦是由旋转的不平衡图案与光晕中引起的密度尾流的重力相互作用引起的。密度尾流是通过傅里叶-拉普拉斯变换求解线性无碰撞玻尔兹曼和泊松方程来确定的。然后，我们发现动态摩擦总是会抑制我们的光环模型中的不平衡图案。此外，阻尼时间比哈勃时间短得多，通常为 1 Gyr，除非图案速度非常慢。考虑到如此短的阻尼时间尺度和观察到的大部分螺旋状不平衡圆盘（例如 ≃30%），所有不平衡圆盘最近都被激发是不可能的。因此，这表明大多数观察到的不平衡圆盘都是非常缓慢旋转的模式。讨论了模式速度慢的弱阻尼模式的重要性。
The effect of dynamical friction on the time evolution of lopsided disks is examined by using linear perturbation theory. The friction is caused by the gravitational interaction of a rotating lopsided pattern with a density wake induced in halos. The density wake is determined by solving the linearized collisionless Boltzmann and Poisson equations by means of the Fourier-Laplace transform. Then, it is found that dynamical friction always damps a lopsided pattern in our halo model. In addition, the damping time is much shorter than a Hubble time, typically 1 Gyr, unless the pattern speed is quite slow. Considering such a short damping timescale and the observed large fraction of lopsided disks in spirals, say, ≃30%, it will be unlikely that all of the lopsided disks are recently excited. Thus, it is suggested that most of the observed lopsided disks are very slowly rotating patterns. The significance of weakly damped modes that have a slow pattern speed is discussed.