Third-Epoch Magellanic Cloud Proper Motions II: The Large Magellanic Cloud Rotation Field in Three Dimensions

摘要

We present the first detailed assessment of the large-scale rotation of anygalaxy based on full three-dimensional velocity measurements. We do this forthe LMC by combining our HST average proper motion (PM) measurements for starsin 22 fields, with existing line-of-sight (LOS) velocity measurements for 6790individual stars. We interpret these data with a model of circular rotation ina flat disk. The PM and LOS data paint a consistent picture of the LMC rotationand their combination yields several new insights. The PM data imply a stellardynamical center that coincides with the HI dynamical center, and a rotationcurve amplitude consistent with that inferred from LOS velocity studies. Theimplied disk viewing angles agree with the range of values found in theliterature, but continue to indicate variations with stellar population and/orradius. Young (RSG) stars rotate faster than old (RGB/AGB) stars due toasymmetric drift. Outside the central region, the circular velocity isapproximately flat at Vcirc = 91.7 +/- 18.8 km/s. This is consistent with thebaryonic Tully-Fisher relation, and implies an enclosed mass M(8.7 kpc) = (1.7+/- 0.7) x 10^10 solar masses. The virial mass is larger and depends on thefull extent of the dark halo. The tidal radius is 22.3 +/- 5.2 kpc (24.0 +/-5.6 degrees). Combination of the PM and LOS data yields kinematic distanceestimates for the LMC, but these are not yet competitive with other methods.