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arXiv · 2108.10867

Stellar kinematics of dwarf galaxies from multi-epoch spectroscopy: application to Triangulum II

Rachel Buttry·Andrew B. Pace·Sergey E. Koposov·Matthew G. Walker·Nelson Caldwell·Evan N. Kirby·Nicolas F. Martin·Mario Mateo·Edward W. Olszewski·Else Starkenburg·Carles Badenes·Christine Mazzola Daher
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Abstract

We present new MMT/Hectochelle spectroscopic measurements for 257 stars observed along the line of sight to the ultra-faint dwarf galaxy Triangulum II. Combining with results from previous Keck/DEIMOS spectroscopy, we obtain a sample that includes 16 likely members of Triangulum II, with up to 10 independent redshift measurements per star. To this multi-epoch kinematic data set we apply methodology that we develop in order to infer binary orbital parameters from sparsely sampled radial velocity curves with as few as two epochs. For a previously-identified (spatially unresolved) binary system in Tri~II, we infer an orbital solution with period $296.0_{-3.3}^{+3.8} \rm~ days$ , semi-major axis $1.12^{+0.41}_{-0.24}\rm~AU$, and a systemic velocity $ -380.0 \pm 1.7 \rm~km ~s^{-1}$ that we then use in the analysis of Tri~II's internal kinematics. Despite this improvement in the modeling of binary star systems, the current data remain insufficient to resolve the velocity dispersion of Triangulum II. We instead find a 95% confidence upper limit of $\sigma_{v} \lesssim 3.4 \rm ~km~s^{-1}$.

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Rachel Buttry, Andrew B. Pace, Sergey E. Koposov, Matthew G. Walker, Nelson Caldwell, Evan N. Kirby, Nicolas F. Martin, Mario Mateo, Edward W. Olszewski, Else Starkenburg, Carles Badenes, Christine Mazzola Daher. 2021-08-24. Stellar kinematics of dwarf galaxies from multi-epoch spectroscopy: application to Triangulum II. https://doi.org/10.1093/mnras/stac1441

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