Top: Sgr B2(N), bottom: Sgr B2(M). The SED convolved with different beam sizes is plotted in blue. For each beam, the combined dust and free-free emission is indicated with the solid blue line, and the contributions from the free-free emission is indicated with the dotted blue line. The τ = 1 surface, i.e. the place along the line-of-sight where the optical depth τ equals one is plotted in orange. Darker colors indicate a smaller beam size.