三轴晕中重子凝聚引起的轨道演化
The Orbital Evolution Induced by Baryonic Condensation in Triaxial Halos
摘要：
使用光谱方法，我们分析了长轴/三轴暗物质（DM）晕的N体模拟的轨道结构，以了解驱动DM晕和椭圆星系的形状的演变过程中，中心质量的增长。一个长期存在的问题是，DM晕形状的变化是否是盒轨道的混沌散射的结果，或者它们是否会随着银河系势的变化而改变形状。我们使用轨道频率来分类轨道，量化轨道形状，并确定共振轨道和混沌轨道。基于频率的方法克服了李雅普诺夫指数对数值离散效应敏感的局限性。无论重子分量的分布如何，DM晕的形状变化主要是由于给定家族中单个轨道形状的变化。具有小的近心半径的轨道比具有大的近心半径的轨道更可能改变它们的轨道类型和形状。演化是规则的（可逆的）还是混沌的（不可逆的），主要取决于重子分量的径向分布。任何形状的扩展重子分量的增长都会导致轨道布居的规则而非混沌的变化。相比之下，一个大规模的和紧凑的中心组件的增长结果在混乱的散射盒和长轴管轨道的一个显着的部分。圆盘的成长会导致相当一部分的晕粒子被主要的全球轨道共振所捕获。尽管DM晕的形状在中心重子分量的增长之后总是相当扁扁的，但其轨道人口的很大一部分具有其三轴或扁长祖先（ABRIDGED）的特征。
英文摘要：
Using spectral methods, we analyse the orbital structure of prolate/triaxial dark matter (DM) halos in N-body simulations to understand the processes that drive the evolution of shapes of DM halos and elliptical galaxies in which central masses are grown. A longstanding issue is whether the change in the shapes of DM halos is the result of chaotic scattering of box orbits, or whether they change shape adiabatically in response to the evolving galactic potential. We use orbital frequencies to classify orbits, to quantify orbital shapes, and to identify resonant orbits and chaotic orbits. The frequency-based method overcomes the limitations of Lyapunov exponents which are sensitive to numerical discreteness effects. Regardless of the distribution of the baryonic component, the shape of a DM halo changes primarily due to changes in the shapes of individual orbits within a given family. Orbits with small pericentric radii are more likely to change both their orbital type and shape than orbits with large pericentric radii. Whether the evolution is regular (and reversible) or chaotic (and irreversible), depends primarily on the radial distribution of the baryonic component. The growth of an extended baryonic component of any shape results in a regular rather than chaotic change in orbital populations. In contrast the growth of a massive and compact central component results in chaotic scattering of a significant fraction of both box and long-axis tube orbits. The growth of a disk causes a significant fraction of halo particles to become trapped by major global orbital resonances. Despite the fact that shape of a DM halo is always quite oblate following the growth of a central baryonic component, a significant fraction of its orbit population has characteristics of its triaxial or prolate progenitor (ABRIDGED).
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