NUMERICAL SIMULATIONS OF THE MAGELLANIC SYSTEM .1. ORBITS OF THE MAGELLANIC CLOUDS AND THE GLOBAL GAS-DISTRIBUTION

The numerical model of the Galaxy and the Large and Small Magellanic Clouds devised by Mural and Fujimoto is employed, with revised values of various observational parameters, to reproduce the global gas distribution in the Magellanic system by a test-particle simulation. The Magellanic orbits that achieve the best reproduction of the Magellanic Stream and the inter-Cloud Bridge place the LMC and the SMC in a binary state for the past 15 Gyr, with a close encounter between the Magellanic Clouds occurring 0.2 Gyr ago at a minimum separation of 7 kpc. By performing a test-particle simulation with 20 000 particles representing the LMC and SMC discs, a detailed comparison can be made with observations of the structure of the Magellanic Clouds and inter-Cloud Bridge. In particular, the large extent in depth of the SMC, shell-like irregularities in the outer part of the LMC, and distinct gas masses in the inter-Cloud Bridge region are shown to result from the tidal interactions of the Magellanic system. The Magellanic Stream is modelled as a product of the tidal interaction of the Magellanic Clouds with the Galaxy, and some criticisms of the standard tidal model for the origin of the Magellanic Stream are addressed.