High reddening patches in Gaia DR2. Possible artifacts or indication of
  star formation at the edge of the Galactic disk
  Context: Deep GALEX UV data show that the extreme outskirts of some spiral
galaxies are teeming with star formation. Such young stellar populations
evolving so far away from the bulk of their host galaxies challenge our overall
understanding of how star formation proceeds at galactic scales. It is at
present unclear whether our own Milky Way may also exhibit ongoing and recent
star formation beyond the conventional edge of the disk ($\sim 15$ kpc). Aims:
Using \textit{Gaia} DR2 data, we aim to determine if such a population is
present in the Galactic halo, beyond the nominal radius of the Milky Way disk.
Methods: We studied the kinematics of \textit{Gaia} DR2 sources with parallax
values between 1/60 and 1/30 milliarcseconds towards two regions that show
abnormally high values of extinction and reddening; the results are compared
with predictions from GALAXIA Galactic model. We also plotted the
color-magnitude (CM) diagrams with heliocentric distances computed inverting
the parallaxes, and studied the effects of the large parallax errors by Monte
Carlo sampling. Results: The kinematics point towards a Galactic origin for one
of the regions, while the provenance of the stars in the other is not clear. A
spectroscopic analysis of some of the sources in the first region confirms that
they are located in the halo. The CM diagram of the sources suggests that some
of them are young.
