Multiple phase spirals suggest multiple origins in Gaia DR3

• Published in: Monthly notices of the Royal Astronomical Society. Letters Vol. 516; no. 1; pp. L7 - L11
• Main Authors: Hunt, Jason A S, Price-Whelan, Adrian M, Johnston, Kathryn V, Darragh-Ford, Elise
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.10.2022
• Subjects: galaxies: structure; galaxies: kinematics and dynamics; Galaxy: structure; methods: numerical
• ISSN: 1745-3925; 1745-3933
• DOI: 10.1093/mnrasl/slac082

ABSTRACT Gaia Data Release 2 revealed that the Milky Way contains significant indications of departures from equilibrium in the form of asymmetric features in the phase space density of stars in the Solar neighbourhood. One such feature is the z–vz phase spiral, interpreted as the response of the disc to the influence of a perturbation perpendicular to the disc plane, which could be external (e.g. a satellite) or internal (e.g. the bar or spiral arms). In this work, we use Gaia Data Release 3 to dissect the phase spiral by dividing the local data set into groups with similar azimuthal actions, Jϕ, and conjugate angles, θϕ, which selects stars on similar orbits and at similar orbital phases, thus having experienced similar perturbations in the past. These divisions allow us to explore areas of the Galactic disc larger than the surveyed region. The separation improves the clarity of the z–vz phase spiral and exposes changes to its morphology across the different action-angle groups. In particular, we discover a transition to two armed ‘breathing spirals’ in the inner Milky Way. We conclude that the local data contain signatures of not one, but multiple perturbations with the prospect to use their distinct properties to infer the properties of the interactions that caused them.