Kinematics beats dust: unveiling nested substructure in the perturbed
  outer disc of the Milky Way
  We use $Gaia$ eDR3 data and legacy spectroscopic surveys to map the Milky Way
disc substructure towards the Galactic Anticenter at heliocentric distances
$d\geq10\,\rm{kpc}$. We report the discovery of multiple previously undetected
new filaments embedded in the outer disc in highly extincted regions. Stars in
these over-densities have distance gradients expected for disc material and
move on disc-like orbits with $v_{\phi}\sim170-230\,\rm{km\,s^{-1}}$, showing
small spreads in energy. Such a morphology argues against a quiescently growing
Galactic thin disc. Some of these structures are interpreted as excited outer
disc material, kicked up by satellite impacts and currently undergoing
phase-mixing ("feathers"). Due to the long timescale in the outer disc regions,
these structures can stay coherent in configuration space over several Gyrs. We
nevertheless note that some of these structures could also be folds in the
perturbed disc seen in projection from the Sun's location. A full 6D
phase-space characterization and age dating of these structure should help
distinguish between the two possible morphologies.
