The Shapes of Galaxies and Their Halos as Traced by Stars: The Milky Way Dark Halo and The LMC Disk

Abstract

Stars and their kinematics provide one of the tools available for studies of the shapes of galaxies and their halos. In this review I focus on two specific applications: the shape of the Milky Way dark halo and the shape of the LMC disk. The former is constrained by a variety of observations, but an accurate determination of the axial ratio q_DH remains elusive. A very flattened Milky Way dark halo with q_DH < 0.4 is ruled out, and values q_DH > 0.7 appear most consistent with the data. Near-IR surveys have revealed that the LMC disk is not approximately circular, as long believed, but instead has an axial ratio of 0.7 in the disk plane. The elongation is perpendicular to the Magellanic Stream, indicating that it is most likely due to the tidal force of the Milky Way. Equilibrium dynamical modeling of galaxies is important for many applications. At the same time, detailed studies of tidal effects and tidal streams have the potential to improve our understanding of both the Milky Way dark halo and the structure of satellite galaxies such as the LMC.