Simulations of the Magellanic Stream in a First Infall Scenario

TL;DR

This paper uses simulations to show that the Magellanic Stream likely formed from tidal interactions between the LMC and SMC before their first infall into the Milky Way, challenging previous models based on repeated orbits.

Contribution

It introduces a novel formation scenario for the Magellanic Stream based on first infall dynamics, supported by N-body/SPH simulations with cosmologically motivated initial conditions.

Findings

The Magellanic Stream can form from LMC-SMC tidal interactions prior to MW infall.

First infall scenario explains the age and structure of the Magellanic Stream.

Simulation results are consistent with recent proper motion measurements.

Abstract

Recent high precision proper motions from the Hubble Space Telescope (HST) suggest that the Large and Small Magellanic Clouds (LMC and SMC, respectively) are either on their first passage or on an eccentric long period (>6 Gyr) orbit about the Milky Way (MW). This differs markedly from the canonical picture in which the Clouds travel on a quasi-periodic orbit about the MW (period of ~2 Gyr). Without a short period orbit about the MW, the origin of the Magellanic Stream, a young (1-2 Gyr old) coherent stream of HI gas that trails the Clouds ~150 degrees across the sky, can no longer be attributed to stripping by MW tides and/or ram pressure stripping by MW halo gas. We propose an alternative formation mechanism in which material is removed by LMC tides acting on the SMC before the system is accreted by the MW. We demonstrate the feasibility and generality of this scenario using an N-body/SPH simulation with cosmologically motivated initial conditions constrained by the observations. Under these conditions we demonstrate that it is possible to explain the origin of the Magellanic Stream in a first infall scenario. This picture is generically applicable to any gas-rich dwarf galaxy pair infalling towards a massive host or interacting in isolation.