The angular momentum spiral of the Milky Way disc in Gaia

TL;DR

This paper introduces a novel angular momentum-based perspective on the Milky Way's phase-space spiral, using Gaia data to model disc perturbations and disequilibrium in six-dimensional phase space.

Contribution

It presents a new angular momentum framework for analyzing the phase-space spiral, linking it to disc perturbations and simplifying the interpretation of disequilibrium in the Milky Way.

Findings

Detected a prominent angular momentum spiral in Gaia DR3 data.

Developed a generative model linking the spiral to past disc tilts.

Model successfully reproduces key features of the observed spiral.

Abstract

Data from the Gaia mission shows prominent phase-space spirals that are the signatures of disequilibrium in the Milky Way (MW) disc. In this work, we present a novel perspective on the phase-space spiral in angular momentum (AM) space. Using Gaia DR3, we detect a prominent AM spiral in the solar neighbourhood. We demonstrate the relation of AM to the $z-v_z$ spiral and show that we can map to this space from angular momentum through simplifying assumptions. By modelling the orbit of stars in AM, we develop a generative model for the spiral where the disc is perturbed by a bulk tilt at an earlier time. Our model successfully describes the salient features of the AM spiral in the data. Modelling the phase spiral in AM is a promising method to constrain both perturbation and MW potential parameters. Our AM framework simplifies the interpretation of the spiral and offers a robust approach to modelling disequilibrium in the MW disc using all six dimensions of phase space simultaneously.