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

Kenji Bekki, Masashi Chiba

Research output: Contribution to journalArticlepeer-review

118 Citations (Scopus)

Abstract

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 disc components as well as the populations of the field stars and star clusters. The main results of the present simulations are as follows. Tidal interaction between the Clouds and the Galaxy during the last 9 Gyr has transformed the initially thin, non-barred LMC disc into three different components: central bar, thick disc and kinematically hot stellar halo. The central bar is composed of both old field stars and newly formed ones, with the two fractions being equal in its innermost part. The final thick disc has central velocity dispersion of ∼30 km s-1 and shows rotationally supported kinematics with Vm0 ∼ 2.3. The stellar halo is formed during the interaction, and consists mainly of old stars originating from the outer part of the initially thin LMC disc. The outer halo shows velocity dispersion of ∼40 km s-1 at a distance of 7.5 kpc from the LMC centre and has a somewhat inhomogeneous distribution of stars. The stellar halo contains relatively young, metal-rich stars with a mass fraction of 2 per cent. Repetitive interaction between the Clouds and the Galaxy has moderately enhanced the star formation rate to ∼0.4 M⊙ yr-1 in the LMC disc. Most of the new stars (∼90 per cent) are formed within the central 3 kpc of the disc, 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. Efficient globular cluster formation does not occur until the LMC starts interacting violently and closely with the SMC (∼3 Gyr ago). The newly formed globular cluster system has a disc-like distribution with rotational kinematics, and its mean metallicity is ∼ 1.2 higher than that of new field stars because of pre-enrichment by the formation of field stars prior to cluster formation. 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 disc 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 past several Gyr.

Original languageEnglish
Pages (from-to)680-702
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Volume356
Issue number2
DOIs
Publication statusPublished - 2005 Jan 11

Keywords

  • Galaxies: haloes
  • Galaxies: kinematics and dynamics
  • Galaxies: star clusters
  • Galaxies: structure
  • Magellanic Clouds

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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