Dark Halo Shapes and the Fate of Stellar Bars
Dark Halo Shapes and the Fate of Stellar Bars
复制标题
暗晕形状和恒星条的命运
DOI：
10.1086/342117
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
I. Shlosman
中科院分区：
文献类型：
--
作者：
A. El;I. Shlosman
我们利用李雅普诺夫指数研究了具有轻度三轴晕的棒状星系中轨迹的稳定性特性。该方法非常适合于截面表面和其他简单诊断不适用的时间相关三维势。我们发现，当光晕集中在中心时，从包含条的平面附近开始的大多数轨迹都会变得混乱。这些轨道的空间密度分布与棒的空间密度分布不匹配，与后者相比，在平面内和平面外过度延伸。此外，许多剩余的规则轨迹的形状与条形密度分布不匹配，太圆了。因此，不太可能找到与时间无关的自洽解。当势的非旋转非轴对称扰动达到10%时，几乎所有积分轨迹都是混沌的并且具有大的李亚普诺夫指数。没有发现与条形对齐的规则轨迹。因此，如果密度图的演化与轨道不稳定的特征时间尺度直接相关，则棒溶解将在几个动力学时间的时间尺度上发生。缓慢旋转的非轴对称对广泛混沌行为开始所需的电势的贡献非常小。即使势轴比为 0.99，也会导致大的连通混沌区域在初始条件空间中占主导地位。因此，由中心集中的轴对称晕和恒星棒组成的系统在结构上似乎不稳定，与完美轴对称性的小偏差（~1%）应该会导致棒在远小于哈勃时间的时间尺度上溶解。由于在大尺度结构的冷暗物质模拟中发现的光晕都是中心集中的和三轴的，嵌入在这种光晕中的星条不太可能形成并存活，除非光晕在重子成分的形成过程中被修改。
We investigate the stability properties of trajectories in barred galaxies with mildly triaxial halos by means of Liapunov exponents. This method is perfectly suitable for time-dependent three-dimensional potentials where surfaces of sections and other simple diagnostics are not applicable. We find that when halos are centrally concentrated most trajectories starting near the plane containing the bar become chaotic. The spatial density distribution of these orbits does not match that of the bar, being overextended in and out of the plane compared to the latter. Moreover, the shape of many of the remaining regular trajectories does not match the bar density distribution, being too round. Therefore, time-independent self-consistent solutions are highly unlikely to be found. When the nonrotating nonaxisymmetric perturbation in the potential reaches 10%, almost all trajectories integrated are chaotic and have large Liapunov exponents. No regular trajectories aligned with the bar have been found. Hence, if the evolution of the density figure is directly related to the characteristic timescale of orbital instability, bar dissolution would take place on a timescale of a few dynamical times. The slowly rotating nonaxisymmetric contribution to the potential required for the onset of widespread chaotic behavior is remarkably small. Even a potential axis ratio of 0.99 results in large connected chaotic regions dominating the space of initial conditions. Systems consisting of centrally concentrated axisymmetric halos and stellar bars thus appear to be structurally unstable, and small (~1%) deviations from perfect axisymmetry should result in a bar dissolution on a timescale significantly smaller than the Hubble time. Since halos found in cold dark matter simulations of large-scale structure are both centrally concentrated and triaxial, it is unlikely that stellar bars embedded in such halos would form and survive unless the halos are modified during the formation of the baryonic component.
DOI：
10.1046/j.1365-8711.1999.02766.x
发表时间：
1998-11
影响因子：
4.8
作者：
R. Abraham;M. Merrifield;R. Ellis;N. Tanvir;J. B. I. O. Astronomy;U. Cambridge;S. O. PhysicsAstronomy;U. Nottingham;D. PhysicsAstronomy;U. Southampton
通讯作者：
R. Abraham;M. Merrifield;R. Ellis;N. Tanvir;J. B. I. O. Astronomy;U. Cambridge;S. O. PhysicsAstronomy;U. Nottingham;D. PhysicsAstronomy;U. Southampton