Images of the integrated intensity (in K km s^-1) of ¹²CO 3 − 2 from the series of representative models (Table 1). Models with δ_gas = 1,10^-2,10^-3 and 10^-4 are shown. The inclination i = 30° and the black dashed lines show the size of the gap (10 < r < 45 AU). Red dashed lines show the radius where PAHs can survive in absence of UV shielding by a dusty inner disk (Sect. 3). Upper panels: models with a dusty inner disk present (δ_dust = 10^-5). Lower panels: models without an inner disk (δ_dust = 10^-10).