The Magellanic Stream at 20 kpc: A New Orbital History for the Magellanic Clouds

TL;DR

This paper presents new simulations of the Magellanic Stream's formation, suggesting it is only about 20 kpc from the Sun, significantly closer than previous models predicted, with implications for its mass, stellar content, and lifetime.

Contribution

The study introduces an updated orbital history incorporating the Magellanic Corona and live Milky Way halo, leading to a paradigm shift in the Stream's estimated distance and properties.

Findings

Stream is approximately 20 kpc from the Sun at closest approach.

Mass estimates of the Stream are reduced by a factor of about 5.

The Stream's lifetime is shortened due to interactions with the MW's hot corona.

Abstract

We present new simulations of the formation of the Magellanic Stream based on an updated first-passage interaction history for the Magellanic Clouds, including both the Galactic and Magellanic Coronae and a live dark matter halo for the Milky Way. This new interaction history is needed because previously successful orbits need updating to account for the Magellanic Corona and the loosely bound nature of the Magellanic Group. These orbits involve two tidal interactions over the last 3.5 Gyrs and reproduce the Stream's position and appearance on the sky, mass distribution, and velocity profile. Most importantly, our simulated Stream is only $\sim$20 kpc away from the Sun at its closest point, whereas previous first-infall models predicted a distance of $100-200$ kpc. This dramatic paradigm shift in the Stream's 3D position would have several important implications. First, estimates of the observed neutral and ionized masses would be reduced by a factor of $\sim$5. Second, the stellar component of the Stream is also predicted to be $<$20 kpc away. Third, the enhanced interactions with the MW's hot corona at this small distance would substantially shorten the Stream's lifetime. Finally, the MW's UV radiation field would be much stronger, potentially explaining the H$\alpha$ emission observed along most of the Stream. Our prediction of a 20 kpc Stream could be tested by searching for UV absorption lines towards distant MW halo stars projected onto the Stream.