Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream
Ting S. Li, Sergey E. Koposov, Denis Erkal, Alexander P. Ji, Nora, Shipp, Andrew B. Pace, Tariq Hilmi, Kyler Kuehn, Geraint F. Lewis, Dougal, Mackey, Jeffrey D. Simpson, Zhen Wan, Daniel B. Zucker, Joss Bland-Hawthorn,, Lara R. Cullinane, Gary S. Da Costa, Alex Drlica-Wagner

TL;DR
This study combines spectroscopic, photometric, and astrometric data to demonstrate that the ATLAS and Aliqa Uma streams are a single, perturbed stellar stream affected by the Sagittarius dwarf galaxy and the Large Magellanic Cloud, revealing complex dynamical interactions.
Contribution
First spectroscopic confirmation that ATLAS and Aliqa Uma are a single stream, with detailed analysis of its perturbations and orbit influenced by external galactic structures.
Findings
ATLAS and Aliqa Uma are one stream with a discontinuity.
The stream's features are consistent with an encounter with Sagittarius dwarf galaxy.
The stream's orbit shows influence from the Large Magellanic Cloud.
Abstract
We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey (), in combination with the photometric data from the Dark Energy Survey and astrometric data from . From the coherence of spectroscopic members in radial velocity and proper motion, we find out that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the "kink" feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf Gyr ago can create a feature similar to the observed "kink". In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the…
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