Gas temperature distribution: Model   1 (UV only) in the left panel, X-ray models with L_X = 10³⁰   erg   s^-1 (model   3), L_X = 10³²   erg   s^-1 (model   5) in the middle and right panel, respectively. Contour lines are plotted over for τ_rad = 1 (radial dust optical depth at 550 nm, dashed line), τ_ver = 1 (vertical dust optical depth at 550 nm, dotted line), and an X-ray optical depth of one at 1 keV (dot-dashed line). The relative positions of these two depths depend strongly on the assumed dust properties (see Table 2). The solid line corresponds to T_gas = 8000 K.