Measuring the Milky Way potential with the phase snail shape curves
Year: 2026
Type: article
Abstract: Phase spirals found in the vertical phase-space (z-V_z) indicate that the Galactic disk is in disequilibrium. Although the origin remains elusive, the wrapping of phase snails is dominated by the vertical potential profiles, naturally encoding potential information in their shapes. We attempt to measure the Galactic potential utilizing the snail shape curves. To measure the Galactic potential, we extracted the phase snail shape curves from density contrast maps and transformed them into the vertical frequency-action angle (Ω_z - þeta_z) space via orbital integration, then performed linear fitting to derive potential parameters. We verified our method with a test particle simulation with the disk perturbation included within the impulse approximation. Our method performs well in the test particle simulation, with the recovered Galactic vertical potential profiles in excellent agreement with the input potential models. We also apply our method to the observed phase snails with guiding center radii in the range of 8łe R_głe11 kpc. Utilizing snail shape curves only, the model derived vertical potential profiles agree with popular Milky Way potential models. The model yields a Galactic virial mass of M_ 200 = 0.81^ +0.22 _ -0.23 12 , ̊m M_⊙ and a local dark matter density of ρ_ dm,⊙ = 0.0076^ +0.0019 _ -0.0021 , -3 , consistent with the literature, but with a flatter rotation curve than the observation. To better constrain the Galactic potential, we further combine the phase snails and the rotation curve. The improved model results in M_ 200 = 0.87^ +0.31 _ -0.33 12 , ̊m M_⊙ and ρ_ dm,⊙ = 0.0097^ +0.0002 _ -0.0009 , -3 . The high precision of ρ_dm,⊙ results from the joint constraints in the solar neighborhood. We also obtain an estimation of the perturbation time in a range of 400-750 Myr with a median of 564 Myr, consistent with recent measurements. Our work demonstrates the wealth of information contained in the phase snails to constrain the Galactic potential and mass distribution. We expect to apply our method to the widely existed phase snails across the disk to explore the 3D potential maps and mass distributions in the future.
Source: Astronomy and Astrophysics
Authors: Rui Guo, Zhao-Yu Li, Juntai Shen, Jie Wang, Shude Mao
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7223235951