盘状星系中的团块迁移：重新审视钱德拉塞卡动力摩擦

中文摘要 AI 辅助

大质量恒星团块被认为会通过动力摩擦向星系中心迁移，对核球增长和盘状星系的结构演化有贡献。尽管经典的钱德拉塞卡形式主义被广泛用于估算团块的旋入时间，但它对于嵌入真实星系盘的延展、演化团块的有效性仍不确定。我们通过孤立盘状星系模拟，在多个轨道周期内识别并追踪单个恒星团块，以此检验该形式主义。我们开发了基于位置和质量的追踪算法，用于追踪长寿命团块，并将观测到的轨道演化与由模拟重子和暗物质质量分布构建的动力摩擦模型的预测结果进行比较。排除初始暂态阶段后，我们识别出9个长寿命团块，其中8个向内迁移，同时损失了初始质量的60%-90%。该分析模型重现了迁移对团块质量和银心半径的整体依赖关系，但对于6个团块，它高估了旋入时间约2-10倍。由于质量损失会减小动力摩擦力，因此无法解释观测到的更快迁移。我们的结果表明，除经典钱德拉塞卡公式的假设外，额外的物理过程，例如团块-团块相互作用、非圆轨道以及随时间变化的盘状势，在调控团块迁移中发挥重要作用。

英文摘要

Massive stellar clumps are thought to migrate toward galactic centers through dynamical friction, contributing to bulge growth and the structural evolution of disk galaxies. While the classical Chandrasekhar formalism is widely used to estimate clump inspiral times, its validity for extended, evolving clumps embedded in realistic galactic disks remains uncertain. We test this formalism using an isolated disk galaxy simulation by identifying and tracking individual stellar clumps over multiple orbital periods. We develop a position- and mass-based tracking algorithm that follows long-lived clumps and compare their measured orbital evolution with predictions from a dynamical friction model constructed from the simulated baryonic and dark matter mass distributions. After excluding the initial transient phase, we identify nine long-lived clumps, eight of which migrate inward while losing 60-90\% of their initial mass. The analytical model reproduces the overall dependence of migration on clump mass and galactocentric radius, but for six clumps it overestimates the inspiral time by factors of $\sim2$-$10$. Since mass loss would reduce the dynamical friction force, it cannot account for the observed faster migration. Our results suggest that additional physical processes, for example clump-clump interactions, non-circular orbits, and the time-dependent disk potential play an important role in regulating clump migration beyond the assumptions of the classical Chandrasekhar formulation.

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15 pages, 12 figures, Submitted to APJ