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−vz 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.
@article{arxiv.2501.04095,
title = {The angular momentum spiral of the Milky Way disc in Gaia},
author = {Rashid Yaaqib and Aneesh P. Naik and Jorge Peñarrubia and Michael S. Petersen},
journal= {arXiv preprint arXiv:2501.04095},
year = {2025}
}