The ringing Large Magellanic Cloud: evidence for a recent dwarf-dwarf collision

Abstract

Galaxy interactions are ubiquitous in the Universe and represent a primary pathway for galaxy growth. Close passages of dwarf galaxies can induce large-scale vertical oscillations in stellar disks, a phenomenon first identified in the Milky Way within the past decade. Here, we use recent red clump distance maps of the Large Magellanic Cloud (LMC) to show that its stellar periphery is vertically offset from the central disk plane by $\sim$1.2 kpc at radii of $\sim$8.5 kpc and exhibits an S-shaped warp reaching $\sim$3.6 kpc at $\sim$11.5 kpc. We compare these observations to an $N$-body simulation of the LMC-Small Magellanic Cloud (SMC) system, in which a direct collision between the Clouds excites vertical oscillations in the outer LMC disk with amplitudes of $\sim$1~kpc and a period of $\sim$600~Myr. The simulated disk best matches the observed vertical structure $\sim$260~Myr after the collision, although this timing depends on the adopted LMC model. At that time, the simulation reproduces the sign and radial onset of the observed offset and the orientation of the warp, but underpredicts the amplitude of the warp by a factor of $\sim$4-5. These results support a collision-driven origin for the large-scale vertical structure of the LMC disk and demonstrate that dwarf--dwarf interactions can reshape stellar disks on galactic scales.