Azimuthal Misalignments in Stellar Warp Structure as Dynamical Tracers of Mergers in Milky Way–like Galaxies

Abstract We investigate the origin of warps in stellar disks using high-resolution Milky Way analogs from the IllustrisTNG50 simulation. Focusing on galaxies that experienced a major merger, we identify a characteristic azimuthal misalignment between the warp structures of stellar populations formed before and after the merger. This misalignment persists even after correcting for differential rotation, suggesting it is a dynamical imprint of the merger rather than a consequence of internal kinematics. In contrast, galaxies without significant merger events show no such offset between stellar populations of different ages. These findings support the scenario in which mergers can induce long-lived warps and leave detectable structural signatures in stellar disks. Applied to the Milky Way, this approach offers a potential way to test whether the Gaia-Sausage-Enceladus merger contributed to the formation of the Galactic warp. It may also provide an independent means to constrain the timing of such merger events by examining the phase offsets in the stellar warp as a function of stellar age.