Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2

TL;DR

This paper introduces a novel method to analyze Gaia DR2 data, revealing six key stellar density structures in the Milky Way, including spiral arms and bar resonances, providing new insights into Galactic dynamics.

Contribution

A new analysis technique applied to Gaia DR2 data that uncovers detailed structures related to spiral arms and bar resonances without relying on specific tracers.

Findings

Identification of six stellar density structures within 5 kpc of the Sun.

Detection of spiral arms consistent with gas and young star observations.

Evidence of bar resonances influencing stellar densities.

Abstract

In this paper we introduce a new method for analysing Milky Way phase-space which allows us to reveal the imprint left by the Milky Way bar and spiral arms on the stars with full phase-space data in Gaia Data Release 2. The unprecedented quality and extended spatial coverage of these data enable us to discover six prominent stellar density structures in the disc to a distance of 5 kpc from the Sun. Four of these structures correspond to the spiral arms detected previously in the gas and young stars (Scutum-Centaurus, Sagittarius, Local and Perseus). The remaining two are associated with the main resonances of the Milky Way bar where corotation is placed at around 6.2 kpc and the outer Lindblad resonance beyond the Solar radius, at around 9 kpc. For the first time we provide evidence of the imprint left by spiral arms and resonances in the stellar densities not relying on a specific tracer, through enhancing the signatures left by these asymmetries. Our method offers new avenues for studying how the stellar populations in our Galaxy are shaped.