The dynamical evolution and star formation history of the Small Magellanic Cloud: effects of interactions with the Galaxy and the Large Magellanic Cloud

Abstract

In order to better understand the dynamical evolution and star formation history of the Magellanic system, realistic N-body simulations of the tidal distortion of the Small Magellanic Cloud (SMC) as a result of the Galaxy and the Large Magellanic Cloud have been carried out, taking into account gas dynamics and star formation processes explicitly. The best model succeeds in reproducing the observed structural, kinematic and star formation properties of the SMC, including other related tidal features in the Magellanic system, without resorting to the ram pressure model. The best-fitting simulation reproduced a gas stream with almost no stars and the observed H I gas fraction, for which the morphology and velocity field agree quite well with those of the Magellanic stream, a result of adopting an initial SMC model that has a compact stellar disc embedded in an extended gaseous disc. This implies that the existence of a purely gaseous Magellanic stream does not poses serious problems to a tidal model of formation. Also, in this best model, the central and south-east side (wing region) of the SMC contained an excess of young stars, as is observed. Comparison with a reference simulation of isolated evolution demonstrated that the acceleration of star formation activity in these regions may be a direct result of the last interaction between the Magellanic Clouds roughly 0.2 Gyr ago, which formed the inter-cloud region. The large extent in depth of the SMC implied by the spatial distribution of Cepheids, and the line-of-sight velocity pattern in H I around the SMC is also reproduced. Finally, the dependences of these results on the numerical parameters that specify the SMC mass model and interstellar gas processes are discussed.