Stellar streams are sensitive laboratories for understanding the small-scale structure in our Galaxy’s gravitational field. Here, we analyze the morphology of the 300 S stellar stream, which has an eccentric, retrograde orbit and thus could be an especially powerful probe of both baryonic and dark substructures within the Milky Way. Due to extensive background contamination from the Sagittarius stream (Sgr), we perform an analysis combining Dark Energy Camera Legacy Survey photometry, 𝐺𝑎𝑖𝑎 DR3 proper motions, and spectroscopy from the Southern Stellar Stream Spectroscopic Survey ( 𝑆 5 ). We redetermine the stream coordinate system and distance gradient, then apply two approaches to describe 300 S ’s morphology. In the first, we analyze stars from 𝐺𝑎𝑖𝑎 using proper motions to remove Sgr. In the second, we generate a simultaneous model of 300 S and Sgr based purely on photometric information. Both approaches agree within their respective domains and describe the stream over a region spanning 33 ∘ . Overall, 300 S has three well-defined density peaks and smooth variations in stream width. Furthermore, 300 S has a possible gap of ∼ 4.7 ∘ and a kink. Dynamical modeling of the kink implies that 300 S was dramatically influenced by the Large Magellanic Cloud. This is the first model of 300 S ’s morphology across its entire known footprint, opening the door for deeper analysis to constrain the structures of the Milky Way.
Cohen et al. (Wed,) studied this question.