Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Benjamin Cohen, Alexander P. Ji, Peter S. Ferguson, Sergey E. Koposov, Alex Drlica-Wagner
| Summary:
Stellar streams are sensitive laboratories for understanding the small-scale
structure in our Galaxy’s gravitational field. Here, we analyze the morphology
of the $300S$ 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, $textit{Gaia}$ DR3 proper motions, and spectroscopy
from the Southern Stellar Stream Spectroscopic Survey ($textit{S}^5$). We
redetermine the stream coordinate system and distance gradient, then apply two
approaches to describe $300S$’s morphology. In the first, we analyze stars from
$textit{Gaia}$ using proper motions to remove Sgr. In the second, we generate
a simultaneous model of $300S$ and Sgr based purely on photometric information.
Both approaches agree within their respective domains and describe the stream
over a region spanning $33^circ$. Overall, $300S$ has three well-defined
density peaks and smooth variations in stream width. Furthermore, $300S$ has a
possible gap of $sim 4.7^circ$ and a kink. Dynamical modeling of the kink
implies that $300S$ was dramatically influenced by the Large Magellanic Cloud.
This is the first model of $300S$’s morphology across its entire known
footprint, opening the door for deeper analysis to constrain the structures of
the Milky Way.
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