Clump Migration in Disk Galaxies: Revisiting Chandrasekhar's Dynamical Friction

Abstract

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.