Weighing the Galactic disk using phase-space spirals

II. Most stringent constraints on a thin dark disk using Gaia EDR3

¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
e-mail: axel.widmark@nbi.ku.dk
² Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
³ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study (UTIAS), The University of Tokyo, Chiba 277-8583, Japan
⁴ The Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁵ Université de Strasbourg, CNRS UMR 7550, Observatoire astronomique de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France

Received: 4 June 2021
Accepted: 5 July 2021

Abstract

Using the method that was developed in the first paper of this series, we measured the vertical gravitational potential of the Galactic disk from the time-varying structure of the phase-space spiral, using data from Gaia as well as supplementary radial velocity information from legacy spectroscopic surveys. For eleven independent data samples, we inferred gravitational potentials that were in good agreement, despite the data samples’ varied and substantial selection effects. Using a model for the baryonic matter densities, we inferred a local halo dark matter density of 0.0085 ± 0.0039 M_⊙ pc⁻³ = 0.32 ± 0.15 GeV cm⁻³. We were also able to place the most stringent constraint on the surface density of a thin dark disk with a scale height ≤50 pc, corresponding to an upper 95% confidence limit of roughly 5 M_⊙ pc⁻² (compared to the previous limit of roughly 10 M_⊙ pc⁻², given the same scale height). For the inferred halo dark matter density and thin dark disk surface density, the statistical uncertainties are dominated by the baryonic model, which potentially could also suffer from a significant systematic error. With this level of precision, our method is highly competitive with traditional methods that rely on the assumption of a steady state. In a general sense, this illustrates that time-varying dynamical structures are not solely obstacles to dynamical mass measurements, but they can also be regarded as assets containing useful information.