2026ApJ...999...79F

Recent observations have revealed that the ion-neutral drift velocity in star-forming molecular clouds and dense cores is on the order of ∼100 m s^–1. Theoretical studies have shown that, in ambipolar diffusion-the process responsible for the differential motion between ions and neutrals-the dust size distribution has a significant impact on the magnetic resistivities. In this study, we perform simulations to investigate how dust growth through accretion and coagulation affects the ion-neutral drift velocity in molecular clouds and cores. We find that, on core scales, both dust growth and a magnetic field strength of 200 μG are required to reproduce the observed drift velocity. We suggest that measurements of ion-neutral drift velocity, particularly on core scales, may serve as a new diagnostic to constrain the dust size distribution and magnetic field strength in such environments.