A Kinematically Cold Structure of Candidate Young OB Stars Toward The
  Anticenter
  We combine GALEX and Gaia DR2 catalogs to track star formation in the
outskirts of our Galaxy. Using photometry, proper motions and parallaxes we
identify a structure of ~ 300 OB-type candidates located between 12 and 15 kpc
from the Galactic center that are kinematically cold. The structure is located
between l = 120 and 200 degrees, above the plane up to ~700 pc and below the
plane to ~ 1 kpc. The bulk motion is disk-like; however we measure a mean
upward vertical motion of 5.7 +-0.4 km/s, and a mean outward radial motion of
between 8 and 16 km/s. The velocity dispersion along the least dispersed of its
proper-motion axes (perpendicular to the Galactic disk) is 6.0 +-0.3 km/s
confirming the young age of this structure.
  While spatially encompassing the outer spiral arm of the Galaxy, this
structure is not a spiral arm. Its explanation as the Milky-Way warp is equally
unsatisfactory. The structure's vertical extent, mean kinematics and asymmetry
with respect to the plane indicate that its origin is more akin to a wobble
generated by a massive satellite perturbing the Galaxy's disk. The mean stellar
ages in this outer structure indicate the event took place some 200 Myr ago.
