Letter to the Editor

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

¹ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstrasse 1, 85748 Garching, Germany
e-mail: sergey.khoperskov@gmail.com
² GEPI, Observatoire de Paris, PSL Université, CNRS, 5 Place Jules Janssen, 92190 Meudon France
³ Sorbonne Université, CNRS UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁴ Volgograd State University, 100 Universitetskii prospect, 400062 Volgograd, Russia
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Received: 6 September 2019
Accepted: 23 December 2019

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 allowed 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.