The LMC’s stellar bar is offset from the outer disk center, tilted from the
disk plane, and does not drive gas inflows. These properties are atypical of
bars in gas-rich galaxies, yet the LMC bar’s strength and radius are similar to
typical barred galaxies. Using N-body hydrodynamic simulations, we show that
the LMC’s unusual bar is explainable if there was a recent (${\approx}$100 Myr
ago) collision (impact parameter $\approx$2 kpc) between the LMC and SMC.
Pre-collision, the simulated bar is centered, co-planar, and has a gaseous
counterpart. Post-collision, the simulated bar is offset ($\approx$1.5 kpc),
tilted ($\approx8.6^\circ$), and non-existent in gas. The simulated bar offset
reduces with time, and comparing with the observed offset ($\approx0.8$ kpc)
suggests the timing of the true collision to be 150-200 Myr ago. 150 Myr
post-collision, the LMC’s bar is centered with its dark matter halo, whereas
the outer disk center is separated from the dark matter center by $\approx1$
kpc. The SMC collision produces a tilted-ring morphology for the simulated LMC,
consistent with observations. Post-collision, the simulated bar’s pattern speed
decreases by a factor of two. Hence, observations of the LMC bar pattern speed
should be interpreted with caution. We demonstrate that the SMC’s torques on
the LMC’s bar during the collision are sufficient to explain the observed bar
tilt, provided the SMC’s total mass within 2 kpc was $(0.8-2.4) \times 10^9$
M$_\odot$. Therefore, the LMC bar’s tilt constrains the SMC’s pre-collision
dark matter profile, and requires the SMC to be a dark matter-dominated galaxy.

Dieser Artikel untersucht Zeitreisen und deren Auswirkungen.

PDF herunterladen: