Multiple phase-spirals suggest multiple origins in Gaia DR3

Jason A. S. Hunt, Adrian M. Price-Whelan, Kathryn V. Johnston, Elise Darragh-Ford

Published 2022-06-13Version 1

Gaia Data Release 2 (DR2) 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 neighborhood. One such feature is the $z-v_z$ phase spiral discovered by Antoja et al. (2018), interpreted as the response of the disk to the influence of a perturbation perpendicular to the disk plane, which could be external (e.g., a satellite) or internal (e.g., the bar or spiral arms). In this work we use Gaia DR3 to dissect the phase spiral by dividing the local data set into groups with similar azimuthal actions, $J_{\phi}$, and angles, ${\theta}_{\phi}$, 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 disk larger than the surveyed region. The separation improves the clarity of the $z-v_z$ phase spiral and exposes changes to its morphology across the different action-angle groups. In particular, we discover an abrupt transition to two armed `breathing spirals' in the inner Milky Way. We conclude that the local data contains signatures of not one, but multiple perturbations with potential to use their distinct properties to infer the properties of the distinct interactions that caused them.