Spiral-like features in the disc revealed by Gaia DR3 radial actions

TL;DR

This study uses Gaia DR3 data to analyze stellar actions in the Milky Way, revealing spiral-like structures and resonances in the Galactic disc that align with known spiral arms and dynamical features.

Contribution

It introduces a new analysis of Gaia DR3 stellar actions, identifying spiral-like features and resonances in the Galactic disc, enhancing understanding of Milky Way dynamics.

Findings

Identification of spiral-like structures in radial action maps.

Detection of a high J_R region at ~10.5 kpc linked to the Outer Lindblad Resonance.

Correlation of stellar dynamical features with known spiral arms.

Abstract

We aim to explore the actions of the new Gaia DR3 astrometry to find structures in the Galactic disc. We compute the actions and the orbital parameters of the Gaia DR3 stars with full astrometry and velocities assuming an axisymmetric model for the Milky Way. Using Gaia DR3 photometric data, we select a subset of giants stars with better astrometry as control sample. The maps of the percentiles of the radial action J_R reveal spiral-like shape structures. We find a high J_R region centered at R~10.5 kpc of 1 kpc width, as well as three arc-shape regions dominated by circular orbits at inner radii. We also identify the spiral arms in the overdensities of the giant population. We find a good agreement with the literature in the innermost region for the Scutum-Sagittarius spiral arms. At larger radii, the low J_R structure tracks the Local arm at negative X, while for the Perseus arm the agreement is restricted to the X<2 kpc region, with a displacement with respect to the literature at more negative longitudes. We detect a high J_R area at a Galactocentric radii of ~10.5 kpc, consistent with some estimations of the Outer Lindblad Resonance location. We conclude that the pattern in the dynamics of the old stars is consistent in several places with spatial distribution of the spiral arms traced by young populations, with small potential contributions from the moving groups.