Formation and evolution of the Magellanic Clouds. I.Origin of structural, kinematical, and chemical properties of the Large Magellanic Cloud

We investigate the dynamical and chemical evolution of the Large Magellanic Cloud (LMC) interacting with the Galaxy and the Small Magellanic Cloud (SMC) based on a series of self-consistent chemodynamical simulations. Our numerical models are aimed at explaining the entire properties of the LMC, i.e., the observed structure and kinematics of its stellar halo and disk components as well as the populations of the field stars and star clusters. The main results of the present simulations are summarized as follows. (1) Tidal interaction between the Clouds and the Galaxy during the last 9 Gyr transforms the initially thin, non-barred LMC disk into the three different components: the central bar, thick disk, and kinematically hot stellar halo. The central bar is composed both of old field stars and newly formed ones with each fraction being equal in its innermost part. The final thick disk has the central velocity dispersion of ∼ 30 km s and shows rotationally supported kinematics with Vm/σ0 ∼ 2.3. (2) The stellar halo is formed during the interaction, consisting mainly of old stars originating from the outer part of the initially thin LMC disk. The outer halo shows velocity dispersion of ∼ 40 km s at the distance of 7.5 kpc from the LMC center and has somewhat inhomogeneous distribution of stars. The stellar halo contains relatively young, metal-rich stars with the mass fraction of 2 %. (3) Repetitive interaction between the Clouds and the Galaxy enhances moderately the star formation rate to ∼ 0.4 M⊙ yr −1 in the LMC disk. Most of the new stars (∼ 90 %) are formed within the central 3 kpc of the disk, in particular, within the central bar for the last 9 Gyr. Consequently, the half mass radius is different by a factor of 2.3 between old field stars and newly formed ones. (4) Efficient globular cluster formation does not occur until the LMC starts interacting violently and closely with the SMC (∼ 3 Gyrs ago). The newly formed globular cluster system has a disky distribution with rotational kinematics and its mean metallicity is ∼ 1.2 higher than that of new field stars because of the pre-enrichment by the formation of field stars prior to cluster formation. (5) The LMC evolution depends on its initial mass and orbit with respect to the Galaxy and the SMC. In particular, the epoch of the bar and thick disk formation and the mass fraction of the stellar halo depend on the initial mass of the LMC. Based on these results, we discuss the entire formation history of the LMC, the possible fossil records of past interaction between the Clouds and the Galaxy, and the star formation history of the SMC for the last several Gyr.