Untangling Magellanic Streams

TL;DR

This study investigates the stellar populations of the Magellanic Stream's different strands, revealing their distinct origins and suggesting the subdominant strand is tidal debris from the Small Magellanic Cloud.

Contribution

It provides the first detailed comparison of stellar populations in different Magellanic Stream strands, linking the subdominant strand to the SMC and tidal origins.

Findings

Subdominant strand contains stars, unlike the dominant strand.

Subdominant strand likely originates from the Small Magellanic Cloud.

The two strands have different origins and are only close in projection.

Abstract

The Magellanic Stream (MS) has long been known to contain multiple H I strands and corresponding stellar populations are beginning to be discovered. Combining a sample of 17 stars from the H3 ("Hectochelle in the Halo at High Resolution") survey with 891 stars drawn from the Gaia DR3 catalog, we trace stars along a sub-dominant strand of the MS, as defined by gas content, across 30$^\circ$ on the sky. We find that the corresponding dominant strand at the similar position along the MS is devoid of stars with Galactocentric distance $\lesssim 55$ kpc while the subdominant strand shows a close correspondence to such stars. We conclude that (1) these two Stream strands have different origins, (2) they are likely only close in projection, (3) the subdominant strand is tidal in origin, and (4) the subdominant strand is composed of "disk" material, gas and stars, with a chemical composition that marginally favors it coming from the Small Magellanic Cloud.