Formation of the off-centre bar in the Large Magellanic Cloud: a collision with a dark satellite?

Recent observations of the structural properties of the Large Magellanic Cloud (LMC) based on the Deep Near-Infrared Southern Sky Survey and Two Micron All-Sky Survey have revealed that the LMC has an off-centre bar even in the older stellar populations. Previous dynamical models including tidal interaction between the LMC, the Small Magellanic Cloud (SMC) and the Galaxy, however, did not reproduce the older off-centre bar so well. Here, we show that the off-centre bar can be formed if the LMC with an already-existing bar can collide with a low-mass Galactic subhalo as massive as ~5 × 10⁸M_solar (roughly corresponding to a few per cent of the LMC mass). The simulated stellar distribution after the collision appears to show an `off-centre bar', not because the centre of the bar significantly deviates from the dynamical centre of the LMC, but because the underlying stellar distribution of the disc is significantly asymmetric with respect to the centre of the bar. We discuss whether off-centre bars observed in Magellanic-type dwarf galaxies can be formed as a result of tidal interaction with low-mass haloes with no or little visible matter.