The phase spiral's origin and evolution: indications from its varying properties across the Milky Way disk

TL;DR

This study investigates the properties and variations of the Milky Way's phase spiral across the disk to understand its origin, evolution, and implications for galactic dynamics, revealing complex structures and smooth variations suggesting a global perturbation source.

Contribution

The paper provides high-resolution spatial maps of the phase spiral, demonstrating its smooth variation across the disk and supporting the hypothesis of a global perturbation origin.

Findings

The phase spiral shows complex structure with respect to radius and azimuth.

Spiral winding and phase vary smoothly across the disk.

Winding time strongly depends on Galactocentric radius.

Abstract

The phase spiral is a perturbation to the vertical phase-space distribution of stars in the Milky Way disk. We study the phase spiral's properties and how they vary with spatial position, in order to constrain its origin and evolution, as well as properties of the disk itself. We produce high resolution maps using two complementary data processing schemes: (a) we bin the Gaia proper motion sample in a disk parallel spatial grid, reaching distances up to 4 kpc; (b) we bin the spatially nearby line-of-sight velocity sample in terms of disk parallel orbital parameters. We find complex structure, most significantly with respect to Galactocentric radius and guiding radius, but also in Galactic azimuth and epicyclic action and phase. We find that spiral winding and rotation phase vary smoothly across the disk, with close-to-flat radial profiles. This uniform structure, in particular for the rotation phase, indicates that the phase spiral was sourced by one or many global perturbations. Curiously, this also implies that the winding time has a strong slope with respect to Galactocentric radius, with low values for the inner disk.