Constraining the Distance to the North Polar Spur with Gaia DR2
  The North Polar Spur (NPS) is one of the largest structures observed in the
Milky Way in both the radio and soft x-rays. While several predictions have
been made regarding the origin of the NPS, modelling the structure is difficult
without precise distance constraints. In this paper, we determine accurate
distances to the southern terminus of the NPS and toward latitudes ranging up
to 55$^{\circ}$. First, we fit for the distance and extinction to stars toward
the NPS using optical and near-infrared photometry and Gaia DR2 astrometry. We
model these per-star distance-extinction estimates as being caused by dust
screens at unknown distances, which we fit for using a nested sampling
algorithm. We then compare the extinction to the Spur derived from our 3D dust
modelling with integrated independent measures from XMM-Newton X-ray absorption
and HI column density measures. We find that we can account for nearly 100% of
the total column density of the NPS as lying within 140 pc for latitudes
$>26^{\circ}$ and within 700 pc for latitudes $< 11^{\circ}$. Based on the
results, we conclude that the NPS is not associated with the Galactic Centre or
the Fermi bubbles. Instead, it is likely associated, especially at higher
latitudes, with the Sco-Cen association.
