Evolution of galaxy shapes from prolate to oblate through compaction events
Evolution of galaxy shapes from prolate to oblate through compaction events
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DOI：
10.1093/mnras/stw606
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发表时间：
2015-12
影响因子：
4.8
通讯作者：
Matteo Tomassetti;A. Dekel;Nir Mandelker;D. Ceverino;S. Lapiner;S. Faber;Omer Kneller;J. Primack
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文献类型：
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作者：
Matteo Tomassetti;A. Dekel;Nir Mandelker;D. Ceverino;S. Lapiner;S. Faber;Omer Kneller;J. Primack
我们利用宇宙学模拟研究星系整体形状的演化。这些形状是指恒星半质量半径处的暗物质（DM）、恒星和气体的成分。大多数星系在 $z\sim2-4$ 处经历特征性压缩事件，形成蓝色金块，这标志着从 DM 主导的中心体到自引力重子核心的转变。我们发现，在高 $z$、DM 主导的阶段，恒星和 DM 系统往往是三轴的，优先长长且相互排列。这种伸长是由各向异性速度色散支持的，该速度色散源于星系沿着主要的大尺度细丝的组装。我们估计，主晕的扭矩能够引起恒星系统的伸长及其与晕的对齐。然后，随着向自重力的转变，小近心轨道膨胀，DM和恒星系统演变成更加球形和扁圆形的结构，与气盘对齐并与旋转相关。这种转变通常发生在恒星质量为 $\sim 10^9$ M$_\odot$ 且核心逃逸速度为 $\sim 100$ km s$^{-1}$ 时，表明超新星反馈可能有效保持核心 DM 主导和系统扁长。早期拉长相本身可能是压实事件的原因，而向扁圆相的转变可能与随后岩心的淬火有关。
We study the evolution of global shapes of galaxies using cosmological simulations. The shapes refer to the components of dark matter (DM), stars and gas at the stellar half-mass radius. Most galaxies undergo a characteristic compaction event into a blue nugget at $z\sim2-4$, which marks the transition from a DM-dominated central body to a self-gravitating baryonic core. We find that in the high-$z$, DM-dominated phase, the stellar and DM systems tend to be triaxial, preferentially prolate and mutually aligned. The elongation is supported by an anisotropic velocity dispersion that originates from the assembly of the galaxy along a dominant large-scale filament. We estimate that torques by the dominant halo are capable of inducing the elongation of the stellar system and its alignment with the halo. Then, in association with the transition to self-gravity, small-pericenter orbits puff up and the DM and stellar systems evolve into a more spherical and oblate configuration, aligned with the gas disc and associated with rotation. This transition typically occurs when the stellar mass is $\sim 10^9$ M$_\odot$ and the escape velocity in the core is $\sim 100$ km s$^{-1}$, indicating that supernova feedback may be effective in keeping the core DM-dominated and the system prolate. The early elongated phase itself may be responsible for the compaction event, and the transition to the oblate phase may be associated with the subsequent quenching in the core.