标题： 星系形成模拟中棒状结构的宇宙演化 显示英文标题

标题： Cosmic evolution of bars in simulations of galaxy formation

摘要： 我们研究了在银河系质量星系形成过程中，由完全自洽流体动力学模拟形成的两个棒状结构的演化。 其中一个星系具有更高的中心质量集中度，并且在$z = 0$时比另一个星系的棒更长、更强。 更强的棒通过主要将角动量传递给暗物质晕而演化。 因此，棒的旋转速度随时间减少，而棒的振幅随时间增加。 虽然这些特征定性上与理想化模拟的结果一致，但我们的棒表现出一些不寻常的行为。 在早期演化阶段，更强棒的图案速度在其半个旋转周期内大幅上下波动。 当棒与$m = 4$模式的傅里叶分量不对齐时，会发生这种不稳定旋转。 尽管弱棒的旋转随时间变慢，但其振幅并未增加。 这一结果与理想化模拟的预期相矛盾，这是由于与质量损失和恒星种群反馈相关的中心密度下降所导致的。 在两个星系中，棒都在$4(\Omega - \Omega_\mathrm{bar}) = \kappa$共振处终止，其中$\Omega$、$\Omega_\mathrm{bar}$和$\kappa$分别是圆轨道的角频率、棒的图案速度和径向角频率。 显示英文摘要

摘要： We investigate the evolution of two bars formed in fully self-consistent hydrodynamical simulations of the formation of Milky Way-mass galaxies. One galaxy shows higher central mass concentration and has a longer and stronger bar than the other at $z = 0$. The stronger bar evolves by transferring its angular momentum mainly to the dark halo. Consequently the rotation speed of the bar decreases with time, while the amplitude of the bar increases with time. While these features qualitatively agree with the results obtained by idealized simulations, our bars show some unusual behaviors. The pattern speed of the stronger bar largely goes up and down within a half revolution in its early evolutionary stage. This unsteady rotation occurs when the bar is misaligned with the $m = 4$ mode Fourier component. The amplitude of the weaker bar does not increase despite the fact that its rotation slows down with time. This result contradicts what is expected from idealized simulations and is caused by the decline of the central density associated with the mass loss and feedback from the stellar populations. In both galaxies, the bars are terminated around $4(\Omega - \Omega_\mathrm{bar}) = \kappa$ resonances, where $\Omega$, $\Omega_\mathrm{bar}$, and $\kappa$ are, respectively, the angular frequency of a circular orbit, the bar patter speed, and the radial angular frequency.