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Milky Way Mass with K Giants and BHB Stars Using LAMOST, SDSS/SEGUE, and Gaia: 3D Spherical Jeans Equation and Tracer Mass Estimator

Published online by Cambridge University Press:  30 October 2025

Sarah A. Bird Open the ORCID record for Sarah A. Bird [Opens in a new window] ,
Xiang-Xiang Xue ,
Chao Liu Open the ORCID record for Chao Liu [Opens in a new window] ,
Chris Flynn ,
Juntai Shen ,
Jie Wang ,
Chengqun Yang ,
Meng Zhai ,
Ling Zhu  and
Gang Zhao
...Show all authors
Sarah A. Bird*
Affiliation:
College of Science, China Three Gorges University, Yichang 443002, People’s Republic of China Center for Astronomy and Space Sciences, China Three Gorges University, Yichang 443002, People’s Republic of China CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030, People’s Republic of China
Xiang-Xiang Xue
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing, 102206, People’s Republic of China
Chao Liu
Affiliation:
Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing, 102206, People’s Republic of China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
Chris Flynn
Affiliation:
Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Post Office Box 218, Hawthorn, VIC 3122, Australia
Juntai Shen
Affiliation:
Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China Key Laboratory for Particle Astrophysics and Cosmology (MOE) / Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai 200240, People’s Republic of China
Jie Wang
Affiliation:
Key Laboratory for Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100101, People’s Republic of China Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing, 102206, People’s Republic of China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
Chengqun Yang
Affiliation:
Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030, People’s Republic of China
Meng Zhai
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, People’s Republic of China
Ling Zhu
Affiliation:
Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030, People’s Republic of China
Gang Zhao
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
Hai-Jun Tian
Affiliation:
School of Science, Hangzhou Dianzi University, Hangzhou, 310018, People’s Republic of China
*
email: sarahbird@ctgu.edu.cn
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Abstract

We measure the enclosed Milky Way (MW) mass profile to Galactocentric distances of ∼70 and ∼50 kpc using the smooth, diffuse stellar halo samples of Bird et al. The samples are Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) K giants (KG) and SDSS/SEGUE blue horizontal branch (BHB) stars with accurate metallicities. The 3D kinematics are available through LAMOST and SDSS/SEGUE distances and radial velocities and Gaia DR2 proper motions. Two methods are used to estimate the enclosed mass: 3D spherical Jeans equation and Evans et al. tracer mass estimator (TME). We remove substructure via the Xue et al. method based on integrals of motion. We evaluate the uncertainties on our estimates due to random sampling noise, systematic distance errors, the adopted density profile, and non-virialization and non-spherical effects of the halo. The tracer density profile remains a limiting systematic in our mass estimates, although within these limits we find reasonable agreement across the different samples and the methods applied. Out to ∼70 and ∼50 kpc, the Jeans method yields total enclosed masses of 4.3±0.95 (random) ±0.6 (systematic) ×1011 M⊙ and 4.1±1.2 (random) ±0.6 (systematic) ×1011 M⊙ for the KG and BHB stars, respectively. For the KG and BHB samples we find a dark matter virial mass of (random) ±0.083 (systematic) ×1012 M⊙ and (random) ±0.15 (systematic) ×1012 M⊙, respectively.

Keywords

stars: individual: BHBstars: individual: K giantsgalaxies: individual: Milky Waystars: kinematics and dynamicsGalaxy: haloGalaxy: kinematics and dynamicsGalaxy: stellar content

Information

Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 19 , Symposium S379: Dynamical Masses of Local Group Galaxies , December 2023 , pp. 79 - 87
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Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of International Astronomical Union

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