Evidence for Tidal Effects in the Stellar Dynamics of the Large Magellanic Cloud

We present a combined analysis of the kinematics of the Large Magellanic Cloud through its H I gas, carbon stars, and red supergiant stars. After correcting the line-of-sight velocities for the recent accurate measurement of the LMC’s space motion, we find that each kinematic tracer clearly defines a flat rotation curve with similar shape but different amplitude for each tracer: 61 km s for the carbon stars, 80 km s for the H I, and 107 km s for the red supergiants. Previously identified tidal H I features are seen to harbor numerous carbon stars, with the tidally disturbed stars comprising 7–15% of the total sample. This discovery implies that we cannot depend on the carbon star sample alone to construct a reliable model of the LMC’s gravitational potential. We also find red supergiants with peculiar kinematics, but their association with tidal features is unclear, and may instead be interacting with supergiant H I shell SGS4. In addition, although the local velocity dispersion of the red supergiants is small, ∼8 km s, their velocity dispersion about the carbon star rotation solution is 17 km s, equal to the velocity dispersion of the carbon stars themselves. We thus appear to be witnessing the tidal heating of the LMC’s stellar disk. Subject headings: stellar dynamics — Magellanic Clouds — galaxies: kinematics and dynamics — stars: carbon — supergiants — ISM: kinematics and dynamics