Simulated surface brightness maps showing thermal X-ray emission ([0.5−2] keV band) from halos in independent 1 × 2 deg² patches derived from direct hydrodynamical simulation (top) and from scaled templates applied to N-body halos (bottom). The largest halo in each image has a mass (M_500c) of 3.8 and 3.1 × 10¹³ M_⊙, top and bottom panels respectively, both are at z = 0.035. The X-ray intensity scale is the same for both images.