The Rotation Curve of the Large Magellanic Cloud and the Implications for Microlensing

The rotation of the disk of the Large Magellanic Cloud (LMC) is derived fromthe radial velocities of 422 carbon stars. New aspects of this analysis includethe propagation of uncertainties in the LMC proper motion with a Monte Carlo,and a self-consistent modeling of the rotation curve and disk kinematics. Therotation curve is well fit by a truncated, finite-thickness exponential diskmodel with no dark halo. The velocity dispersion in radial bins decreases from22 to 15 km/s, then increases to 20 km/s at larger radii. Constant-thicknessmodels in virial equilibrium cannot be reconciled with the data even if theeffects of LMC or Galactic dark halos are included. If the disk is virialized,the LMC disk is flared. We model the velocity dispersion at large radii (R > 6kpc) as a maximal flared disk under the influence of the Galactic dark halo,which favors a mean density for the latter of 0.00025 M_sol/pc^3 at the LMCdistance. LMC stellar kinematics play an important role in elucidating thenature of MACHOs, a dark population inferred from LMC microlensing. We haveconstructed a truncated and flared maximal disk model for the LMC which iskinematically based. Our model does not include a nonvirialized component suchas tidal debris. Our upper limit on the self-lensing optical depth is in goodagreement with that obtained from less sophisticated models, and is an order ofmagnitude too small to account for the MACHO microlensing signal [Abridged].Comment: Accepted for publication in The Astrophysical Journal, 40 pages, 9 figure