Left: galactic neutral hydrogen density column estimated in the neighbourhood of A2163, with contours of the [0.5–2] keV XMM-Newton –EPIC emission overlaid. Right: correlation factor, , relating IR emissivity to the Galactic N_H in a 5 square degree region of the sky centred on A2163. IR emissivity and Galactic N_H have been corrected for dependence on galactic latitude following the analytic approach of Desert et al. (1988). A correlation factor is computed between the average residual IR emissivity and Galactic N_H within sky regions corresponding to a fixed N_H interval of width δN_H = 10²¹   m^-2.