Sifting for a Stream: The Morphology of the $300S$ Stellar Stream

Journal Article · Wed Apr 22 00:00:00 UTC 2026 · The Open Journal of Astrophysics

DOI: https://doi.org/10.33232/001c.161089 · OSTI ID:3157839

Cohen, Benjamin  ^[1]; Ji, Alexander P.  ^[2]; Ferguson, Peter S.  ^[3]; Koposov, Sergey E.  ^[4]; Drlica-Wagner, Alex  ^[5]; Li, Andrew P.  ^[6]; Li, Ting S.  ^[7]; Cullinane, Lara R.  ^[8]; Da Costa, Gary S.  ^[9]; Erkal, Denis  ^[10]; Kuehn, Kyler  ^[11]; Lewis, Geraint F.  ^[12]; Martell, Sarah L.  ^[13]; Pace, Andrew B.  ^[14]; Zucker, Daniel B.  ^[15]; Awad, Petra  ^[16]; Bland-Hawthorn, Joss  ^[17]; Limberg, Guilherme  ^[1]; Martínez-Vázquez, Clara E.  ^[18]; Simon, Joshua D.  ^[19] ; Yang, Yong  ^[12]

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1. University of Chicago
2. University of Chicago; University of Chicago
3. University of Washington
4. University of Edinburgh; University of Cambridge
5. University of Chicago; University of Chicago; Fermi National Accelerator Laboratory
6. University of Toronto
7. University of Toronto; University of Toronto; University of Toronto
8. Leibniz-Institut für Astrophysik Potsdam (AIP)
9. Australian National University; Centre of Excellence for All-Sky Astrophysics in Three Dimensions (ASTRO 3D)
10. University of Surrey
11. Lowell Observatory
12. University of Sydney
13. Centre of Excellence for All-Sky Astrophysics in Three Dimensions (ASTRO 3D); University of New South Wales
14. University of Virginia
15. Macquarie University; Macquarie University Research Centre for Astrophysics and Space Technologies
16. Leiden University
17. Centre of Excellence for All-Sky Astrophysics in Three Dimensions (ASTRO 3D); University of Sydney
18. NSF NOIRLab
19. Observatories of the Carnegie Institution for Science

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, $Gaia$ DR3 proper motions, and spectroscopy from the Southern Stellar Stream Spectroscopic Survey (S⁵). 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 $Gaia$ 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° . Overall, $300S$ has three well-defined density peaks and smooth variations in stream width. Furthermore, $300S$ has a possible gap of ~4.7 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.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: 89243024CSC000002
• OSTI ID: 3157839
• Report Number(s): FERMILAB-PUB-26-0295-PPD; oai:inspirehep.net:3149164; arXiv:2506.21410
• Journal Information: The Open Journal of Astrophysics, Journal Name: The Open Journal of Astrophysics Vol. 9; ISSN 2565-6120
• Publisher: Maynooth Academic PublishingCopyright Statement
• Country of Publication: United States
• Language: English