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

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

Abstract

We present new MMT/Hectochelle spectroscopic measurements for 257 stars observed along the line of sight to the ultrafaint dwarf galaxy Triangulum II (Tri II). Combining results from previous Keck/DEIMOS spectroscopy, we obtain a sample that includes 16 likely members of Tri 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^(+3.8)_(−3.3)⁠, semimajor axis 1.12^(+0.41)_(−0.24)⁠, and systemic velocity −380.0±1.7 km s⁻¹ that we then use in the analysis of Tri II's internal kinematics. Despite this improvement in the modelling of binary star systems, the current data remain insufficient to resolve the velocity dispersion of Tri II. We instead find a 95 per cent confidence upper limit of σ_v≲3.4 km s⁻¹.

Additional Information

© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2022 May 14. Received 2022 May 13; in original form 2021 August 25. Published: 30 May 2022. This work is supported in part by National Science Foundation (NSF) grants AST-1813881 and AST-1909584. ENK is supported by NSF grant AST-1847909, and he gratefully acknowledges support from a Cottrell Scholar award administered by the Research Corporation for Science Advancement. EO is partially supported by NSF grant AST-1815767. NC is supported by NSF grant AST-1812461. MM is supported by U.S. NSF grants AST-1312997, AST-1726457 and AST-1815403. ES acknowledges funding through VIDI grant 'Pushing Galactic Archaeology to its limits' (with project number VI.Vidi.193.093), which is funded by the Dutch Research Council (NWO). CB and CMD are supported by NSF grant AST-1909022. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. This research has made use of NASA's Astrophysics Data System Bibliographic Services. This paper made use of the Whole Sky Database (wsdb) created by Sergey Koposov and maintained at the Institute of Astronomy, Cambridge by Sergey Koposov, Vasily Belokurov, and Wyn Evans with financial support from the Science & Technology Facilities Council (STFC) and the European Research Council (ERC). Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission. New observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Data Availability: The processed MMT/Hectochelle catalog for Tri II targets are publicly available at the Zenodo database, https://doi.org/10.5281/zenodo.6561483.

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