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