The large-scale kinematics of young stars in the Milky Way disc: First results from SDSS-V
Journal article, 2025
We present a first large-scale kinematic map of ∼50 000 young OB stars (Teff ≥ 10 000 K), based on BOSS spectroscopy from the Milky Way Mapper OB programme in the ongoing Sloan Digital Sky Survey V (SDSS-V). Using photogeometric distances, line-of-sight velocities, and Gaia DR3 proper motions, we mapped 3D galactocentric velocities across the Galactic plane to ∼ 5 kpc from the Sun, with a focus on radial motions (vR ). Our results reveal mean radial motion with amplitudes of ±30 km/s that are coherent on kiloparsec scales, alternating between inward and outward motions. These v̄ R amplitudes are considerably higher than those observed for older red-giant populations. These kinematic patterns show only a weak correlation with spiral arm over-densities. Age estimates, derived from MIST isochrones, indicate that 85% of the sample is younger than ∼300 Myr and that the youngest stars (≤30 Myr) align well with density enhancements. The age-dependent v̄R in Auriga makes it plausible that younger stars exhibit different velocity variations than older giants. The origin of the radial-velocity features remains uncertain, and it may result from a combination of factors, including spiral-arm dynamics, the Galactic bar, resonant interactions, or phase mixing following a perturbation. The present analysis is based on approximately one-third of the full target sample. The completed survey will enable a more comprehensive investigation of these features and a detailed dynamical interpretation.
Galaxy: kinematics and dynamics
stars: early-type
Galaxy: disk
Galaxy: structure
Author
Eleonora Zari
University of Florence
Jaime Villaseñor
Max Planck Society
Marina Kounkel
University of North Florida
H. W. Rix
Max Planck Society
Neige Frankel
Canadian Institute for Theoretical Astrophysics
University of Toronto
A. Tkachenko
KU Leuven
Sergey Khoperskov
Leibniz Institute for Astrophysics Potsdam
E. Donghia
University of Wisconsin Madison
A. Roman-Lopes
University of La Serena
Carlos G. Román-Zúñiga
Universidad Nacional Autónoma de México
Guy S. Stringfellow
University of Colorado
Jonathan Tan
Chalmers, Space, Earth and Environment
University of Virginia
Aida Wofford
Universidad Nacional Autónoma de México
Dmitry Bizyaev
Moscow State University
Apache Point Observatory
John Donor
Texas Christian University
José G. Fernández-Trincado
Universidad Catolica del Norte
Sean Morrison
University of Illinois
Kaike Pan
Apache Point Observatory
S. Sánchez
Universidad Nacional Autónoma de México
Andrew Saydjari
Princeton University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 703 A303Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202556444