On the distance to the North Polar Spur and the local CO-H2 factor
  Most models identify the X-ray bright North Polar Spur (NPS) with a hot
interstellar (IS) bubble in the Sco-Cen star-forming region at $\simeq$130 pc.
An opposite view considers the NPS as a distant structure associated with
Galactic nuclear outflows. Constraints on the NPS distance can be obtained by
comparing the foreground IS gas column inferred from X-ray absorption to the
distribution of gas and dust along the line of sight. Absorbing columns towards
shadowing molecular clouds simultaneously constrain the CO-H$_{2}$ conversion
factor. We derived the columns of X-ray absorbing matter NH(abs) from spectral
fitting of dedicated XMM-Newton observations towards the NPS southern terminus
(l=29{\deg}, b=+5 to +11{\deg}). The IS matter distribution was obtained from
absorption lines in stellar spectra, 3D dust maps and emission data, including
high spatial resolution CO measurements recorded for this purpose. NH(abs)
varies from $\simeq$ 4.3 to $\simeq$ 1.3 x 10$^{21}$ cm$^{-2}$ along the 19
fields. Relationships between X-ray brightness, absorbing column and hardness
ratio demonstrate a brightness decrease with latitude governed by increasing
absorption. The comparison with absorption data, local and large-scale dust
maps rules out a NPS near side closer than 300 pc. The correlation between
NH(abs) and the reddening increases with the sightline length from 300 pc to 4
kpc and is the tightest with Planck $\tau_{353}$-based reddening, suggesting a
much larger distance. N(H)/E(B-V) $\simeq$ 4.1 x 10$^{21}$ cm$^{-2}$
mag$^{-1}$. NH(abs) absolute values are compatible with HI-CO clouds at -5
$\leq$ V(LSR) $\leq$ +25 to +45 km s$^{-1}$ and a NPS potentially far beyond
the Local Arm. A molecular cloud shadow at b=+9deg constrains X$_{CO}$ to
$\leq$ 1.0 x 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s. The average X$_{CO}$ is
$\leq$ 0.75 x 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s.
