Discovery of Magellanic Stellar Debris in the H3 Survey

TL;DR

This paper reports the discovery of 15 stars in the Milky Way's outer halo that are likely remnants of past interactions with the Magellanic Clouds, providing new insights into the Magellanic Stream's stellar component.

Contribution

It presents the first identification of Magellanic stellar debris in the Milky Way's halo, linking stars to the Magellanic Stream and past tidal interactions.

Findings

15 stars associated with the Magellanic Stream identified

Stars have velocities and metallicities consistent with SMC origin

Supports the existence of a stellar component in Magellanic tidal debris

Abstract

We report the discovery of 15 stars in the H3 survey that lie, in projection, near the tip of the trailing gaseous Magellanic Stream (MS). The stars have Galactocentric velocities $< -155$ km s$^{-1}$, Galactocentric distances of $\approx 40$ to 80 kpc (increasing along the MS), and [Fe/H] consistent with that of stars in the Small Magellanic Cloud. These 15 stars comprise 94% (15 of 16) of the H3 observed stars to date that have $R_{GAL} > 37.5$ kpc, $-$350 km s$^{-1} < V_{GSR} < -155$ km s$^{-1}$, and are not associated with the Sagittarius Stream. They represent a unique portion of the Milky Way's outer halo phase space distribution function and confirm that unrelaxed structure is detectable even at radii where H3 includes only a few hundred stars. Due to their statistical excess, their close association with the MS and H I compact clouds in the same region, both in position and velocity space, and their plausible correspondence with tidal debris in a published simulation, we identify these stars as debris of past Magellanic Cloud encounters. These stars are evidence for a stellar component of the tidal debris field far from the Clouds themselves and provide unique constraints on the interaction.