The Origin of the Magellanic Stream and Its Leading Arm

TL;DR

This study uses HI velocity profiles to analyze the Magellanic Stream, revealing its origin in the Large Magellanic Cloud and suggesting gas outflows from supergiant shells influence its formation.

Contribution

It identifies the Magellanic Stream's filaments as originating from the LMC's SEHO, challenging previous beliefs that they came from the SMC or Magellanic Bridge.

Findings

At least half of the Stream and most of the Leading Arm originate in the LMC.

The Stream's age is approximately 1.74 billion years.

Gas outflows from supergiant shells in the LMC contribute to the Stream's formation.

Abstract

We explore the Magellanic Stream (MS) using a Gaussian decomposition of the HI velocity profiles in the Leiden-Argentine-Bonn (LAB) all-sky HI survey. This decomposition exposes the MS to be composed of two filaments distinct both spatially (as first pointed out by Putman et al.) and in velocity. Using the velocity coherence of the filaments, one can be traced back to its origin in what we identify as the SouthEast HI Overdensity (SEHO) of the Large Magellanic Cloud (LMC), which includes 30 Doradus. Parts of the Leading Arm (LA) can also be traced back to the SEHO in velocity and position. Therefore, at least one-half of the trailing Stream and most of the LA originates in the LMC, contrary to previous assertions that both the MS and the LA originate in the Small Magellanic Cloud (SMC) and/or in the Magellanic Bridge. The two MS filaments show strong periodic, undulating spatial and velocity patterns that we speculate are an imprint of the LMC rotation curve. If true, then the drift rate of the Stream gas away from the Magellanic Clouds is ~49 km/s and the age of the MS is ~1.74 Gyr. The Staveley-Smith et al. high-resolution HI data of the LMC show gas outflows from supergiant shells in the SEHO that seem to be creating the LA and LMC filament of the MS. Blowout of LMC gas is an effect not previously accounted for but one that probably plays an important role in creating the MS and LA.