Where in the Milky Way is the North Polar Spur

A series of pointed observations with XMM-Newton of the X-ray bright "North Polar Spur” (*) near l=30° and b=8° have been analyzed in combination with dedicated ground-based absorption measurements and three-dimensional reddening maps. There is compelling evidence that the southern terminus of the North Spur is absorption bounded and that the X-ray emitting region is behind the Aquila Rift clouds, at least hundreds of parsecs away. Moreover, absorbing columns deduced from X-ray spectral fitting correlate more tightly with dust optical depths from Planck than with any other ISM column indicator, suggesting that the emission may originate several kpc away. This result raises the question of a possible link between the Spur and outflows from the inner Galaxy (Fermi bubbles, Galactic wind).