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arXiv 1310.0403astro-ph.GAastro-ph.CO
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圆盘星系的长期演化

Secular Evolution in Disk Galaxies

J. A. Sellwood

摘要:

盘星系随着时间的推移,通过过程,可能会重新安排径向质量分布和金属丰度分布在磁盘上。对这种缓慢变化的回顾虽然不完全,但主要限于内部驱动的过程,这些过程可以与星系相互作用驱动的演化区分开来。它既描述了我们目前对磁盘演化的理解,又确定了需要更多工作的领域。恒星盘通过螺旋散射加热,这增加了平面内的随机运动分量,而分子云则将一部分随机能量重定向到垂直运动中。最近发现的在瞬变螺旋模式的共转共振下的径向迁移过程并没有改变盘的基本结构,因为它既没有加热盘也没有使其扩散,但它确实对盘星之间金属丰度的预期分布产生了深远的影响。盘中的条被认为是长期演化的主要驱动力,通过与外盘和晕的相互作用。一旦构成星系盘的物质转化为恒星,它们的整体角动量分布就不会发生太大变化,但气体的角动量分布通常更容易重新排列,从而形成环和伪凸起。虽然模拟是强大的工具,我们已经学到了很多,那些磁盘可能会遭受碰撞松弛,需要谨慎解释一些结果。

英文摘要:

Disk galaxies evolve over time through processes that may rearrange both the radial mass profile and the metallicity distribution within the disk. This review of such slow changes is largely, though not entirely, restricted to internally-driven processes that can be distinguished from evolution driven by galaxy interactions. It both describes our current understanding of disk evolution, and identifies areas where more work is needed. Stellar disks are heated through spiral scattering, which increases random motion components in the plane, while molecular clouds redirect some fraction of the random energy into vertical motion. The recently discovered process of radial migration at the corotation resonance of a transient spiral mode does not alter the underlying structure of the disk, since it neither heats the disk nor causes it to spread, but it does have a profound effect on the expected distribution of metallicities among the disk stars. Bars in disks are believed to be major drivers of secular evolution through interactions with the outer disk and with the halo. Once the material that makes up galaxy disks is converted into stars, their overall angular momentum distribution cannot change by much, but that of the gas is generally far more liable to rearrangement, allowing rings and pseudo-bulges to form. While simulations are powerful tools from which we have learned a great deal, those of disks may suffer from collisional relaxation that requires some results to be interpreted with caution.

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