Kinematic Map of the Galactic Bulge Using HST Proper Motions
Abstract
Constraining the Galactic bulge's non-axisymmetric dynamics requires proper motions in deep fields across many sightlines, yet crowding and extinction limit such measurements. Using multi-epoch observations of 27 fields in the southern Galactic bulge (-6∘ < l < 4∘, -5∘ < b < -1∘) from the ultraviolet-visible (UVIS) channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) with time baselines of 3 to 13 years, and combining them with the absolute proper motion reference frame provided by Gaia Data Release 3 (DR3), we measure absolute proper motions for ~ 400,000 stars. Colour-magnitude diagrams are used to separate bulge stars from foreground disc stars, identify red clump stars and correct for interstellar extinction and reddening. Statistical analysis shows that the mean proper motion in Galactic latitude is consistent with that of the central supermassive black hole Sgr A*, while the mean proper motion in Galactic longitude is affected by disc stars but agrees with Sgr A* after extrapolation to the Galactic plane. Proper motion dispersions increase towards the Galactic centre and are asymmetric across Galactic longitude, with a steeper gradient for l < 0∘, revealing the bulge's non-axisymmetric bar structure. The velocity distribution shows clear anisotropy (σl/σb = 1.131 ± 0.005). The normalised covariance is negative in the l > 0∘ region (~ -0.085) and close to zero in the l < 0∘ region. The proper motion distributions are non-Gaussian in both Galactic longitude and latitude, mainly due to contamination by foreground disc stars.
Related
- Stellar proper motions compared with the plane-of-sky magnetic field
- A posteriori correction of Gaia CRF proper motions using conditional probability and zero-parallax prior
- Euclid Quick Data Release (Q2) -- The Euclid Galactic Bulge Survey
- Observing the Peculiar Acceleration of our Solar System with Quasar Proper Motions
- HURACAN: A comparison of stellar and interstellar proper motions inside L1688
BibTeX
@misc{wang2026kinematic,
title = {{Kinematic Map of the Galactic Bulge Using HST Proper Motions}},
author = {Zhenhao Wang and Shude Mao and Hongjing Yang and Andrzej Udalski and Weicheng Zang and T. Dex Bhadra},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.41395},
eprint = {2610.41395},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.41395},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Kinematic Map of the Galactic Bulge Using HST Proper Motions
AU - Zhenhao Wang
AU - Shude Mao
AU - Hongjing Yang
AU - Andrzej Udalski
AU - Weicheng Zang
AU - T. Dex Bhadra
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2610.41395
UR - https://arxiv.org/abs/2610.41395
AB - Constraining the Galactic bulge's non-axisymmetric dynamics requires proper motions in deep fields across many sightlines, yet crowding and extinction limit such measurements. Using multi-epoch observations of 27 fields in the southern Galactic bulge (-6^∘ < l < 4^∘, -5^∘ < b < -1^∘) from the ultraviolet-visible (UVIS) channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) with time baselines of 3 to 13 years, and combining them with the absolute proper motion reference frame provided by Gaia Data Release 3 (DR3), we measure absolute proper motions for ~ 400,000 stars. Colour-magnitude diagrams are used to separate bulge stars from foreground disc stars, identify red clump stars and correct for interstellar extinction and reddening. Statistical analysis shows that the mean proper motion in Galactic latitude is consistent with that of the central supermassive black hole Sgr A*, while the mean proper motion in Galactic longitude is affected by disc stars but agrees with Sgr A* after extrapolation to the Galactic plane. Proper motion dispersions increase towards the Galactic centre and are asymmetric across Galactic longitude, with a steeper gradient for l < 0^∘, revealing the bulge's non-axisymmetric bar structure. The velocity distribution shows clear anisotropy (σ_l/σ_b = 1.131 ± 0.005). The normalised covariance is negative in the l > 0^∘ region (~ -0.085) and close to zero in the l < 0^∘ region. The proper motion distributions are non-Gaussian in both Galactic longitude and latitude, mainly due to contamination by foreground disc stars.
ER -