Run SimS: gas mass surface density (left) and B-Cousins surface brightness (right) in the central ±1 kpc for t< 0.7 Gyr. Isocontours are spaced by 0.15 mag in log M_⊙ pc^-2 for the gas and 0.5 Bmag pc^-2 for the stars. The map resolution is 10 pc. Gas particles have been convolved by the SPH kernel to obtain the real distribution. Gas surface densities below 1 M_⊙ pc^-2 are contoured with dashed lines. The straight dotted line is the primary bar position-angle.