The outer disc in shambles: blind detection of Monoceros and ACS with
  Gaia's astrometric sample
  The astrometric sample of Gaia allows us to study the outermost Galactic
disc, the halo and their interface. It is precisely at the very edge of the
disc where the effects of external perturbations are expected to be the most
noticeable. Our goal is to detect the kinematic substructure present in the
halo and at the edge of the Milky Way (MW) disc, and provide observational
constraints on their phase-space distribution. We download, one HEALpix at a
time, the proper motion histogram of distant stars, to which we apply a Wavelet
Transformation to reveal the significant overdensities. We then analyse the
large coherent structures that appear in the sky. We reveal a sharp yet complex
anticentre dominated by Monoceros (MNC) and the Anticentre Stream (ACS) in the
north, which we find with an intensity comparable to the Magellanic clouds and
the Sagittarius stream, and by MNC south and TriAnd at negative latitudes. Our
method allows us to perform a morphological analysis of MNC and ACS, both
spanning more than 100$^\circ$ in longitude, and to provide a high purity
sample of giants with which we track MNC down to latitudes as low as
$\sim$5$^\circ$. Their colour-magnitude diagram is consistent with extended
structures at a distance of $\sim$10-11 kpc originated in the disc, with a very
low ratio of RR Lyrae over M giants, and kinematics compatible with the
rotation curve at those distances or only slightly slower. We present a precise
characterisation of MNC and ACS, two previously known structures that our
method reveals naturally, allowing us to detect them without limiting ourselves
to a particular stellar type and, for the first time, using only kinematics.
Our results allow future studies to model their chemo-dynamics and evolution,
thus constraining some of the most influential processes that shaped the MW.
