Optical depth at 9.7 μm, τ_9.7 versus logarithmic of the hydrogen column density at X-rays, N_H. N_H in units of cm^-2. T-ReCS data are shown as blue-filled circles and the Spitzer/IRS data included in our work are shown as empty circles. The object without reported X-ray measurement is labelled as a short line in the Y-axis. Low limits on the N_H are shown as right arrows. Compton-thick sources reported by Goulding et al. (2012) are shown as open squares, and AGN observed with VISIR/VLT by Hönig et al. (2010a) are shown as black-filled stars. Constant gas-to-dust ratio (i.e. the uniform dusty torus) assuming the viewing angles of i = 0,40,80° are shown with the continuous, dashed, and dot-dashed lines, respectively.