The Galactic rotation curve from the ALS III catalogue of OB Stars
Abstract
The Galactic rotation curve reveals the radial mass distribution of the Milky Way, but its determination depends on the tracer population. Young massive stars are the least dynamically evolved tracer, retaining the kinematics of the gas from which they formed, yet previous determinations from OB stars were confined to the solar neighbourhood. We determine the rotation curve and the solar motion from 14017 spectroscopically confirmed OB stars from the ALS III catalogue, using Gaia DR3 five-dimensional astrometry with revised distances and corrected proper motions. The curve is parameterised as a fourth-degree Chebyshev polynomial in Galactocentric radius and fitted to the proper motions by weighted least squares, solving simultaneously for the solar motion. Uncertainties are derived from 1000 bootstrap resamplings. We obtain a circular velocity at the solar radius (8.178 kpc) of 236.3 +/- 1.1 km/s, solar motion components U = 8.06 +/- 0.41, V = 10.91 +/- 0.86 and W = 7.53 +/- 0.14 km/s, and Oort constants A = 16.35 +/- 0.21 and B = -12.54 +/- 0.19 km/s/kpc. The curve rises inside the solar circle and declines gently beyond it, with a local gradient of -3.81 +/- 0.38 km/s/kpc, and is constrained between 5.5 and 11 kpc. Because the tracer is dynamically cold and the proper motions are fitted directly, no asymmetric drift correction or Jeans modelling is required, so the systematics differ from those affecting older tracers. The gentle decline beyond the solar radius agrees with determinations from older tracers where they overlap, making it unlikely to be a methodological artefact. Only the solar radial motion is poorly constrained by tangential data, without affecting the curve. The stars departing most from the curve (1474 to 1662, depending on the selection criterion) form the largest sample of OB runaway candidates to date, to be analysed in a forthcoming paper based on Gaia DR4.
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BibTeX
@misc{berlanas2026galactic,
title = {{The Galactic rotation curve from the ALS III catalogue of OB Stars}},
author = {S. R. Berlanas and M. Pantaleoni González and J. Maíz Apellániz},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32537},
eprint = {2610.32537},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32537},
}
RIS
TY - UNPB
TI - The Galactic rotation curve from the ALS III catalogue of OB Stars
AU - S. R. Berlanas
AU - M. Pantaleoni González
AU - J. Maíz Apellániz
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32537
UR - https://arxiv.org/abs/2610.32537
AB - The Galactic rotation curve reveals the radial mass distribution of the Milky Way, but its determination depends on the tracer population. Young massive stars are the least dynamically evolved tracer, retaining the kinematics of the gas from which they formed, yet previous determinations from OB stars were confined to the solar neighbourhood. We determine the rotation curve and the solar motion from 14017 spectroscopically confirmed OB stars from the ALS III catalogue, using Gaia DR3 five-dimensional astrometry with revised distances and corrected proper motions. The curve is parameterised as a fourth-degree Chebyshev polynomial in Galactocentric radius and fitted to the proper motions by weighted least squares, solving simultaneously for the solar motion. Uncertainties are derived from 1000 bootstrap resamplings. We obtain a circular velocity at the solar radius (8.178 kpc) of 236.3 +/- 1.1 km/s, solar motion components U = 8.06 +/- 0.41, V = 10.91 +/- 0.86 and W = 7.53 +/- 0.14 km/s, and Oort constants A = 16.35 +/- 0.21 and B = -12.54 +/- 0.19 km/s/kpc. The curve rises inside the solar circle and declines gently beyond it, with a local gradient of -3.81 +/- 0.38 km/s/kpc, and is constrained between 5.5 and 11 kpc. Because the tracer is dynamically cold and the proper motions are fitted directly, no asymmetric drift correction or Jeans modelling is required, so the systematics differ from those affecting older tracers. The gentle decline beyond the solar radius agrees with determinations from older tracers where they overlap, making it unlikely to be a methodological artefact. Only the solar radial motion is poorly constrained by tangential data, without affecting the curve. The stars departing most from the curve (1474 to 1662, depending on the selection criterion) form the largest sample of OB runaway candidates to date, to be analysed in a forthcoming paper based on Gaia DR4.
ER -