Top: examples of 2D Gaussian structures injected on top of an fBm image with β = 2.4. The maps only differ in the values of the exponent ψ. All other parameters have the same values (see text for details). All synthetic maps are convolved with a beam whose FWHM = 18.2′′. Bottom: Δ-variance spectrum spectra of the synthetic models for the three cases with ψ = 2, 2.5, and 3. Each synthetic spectrum is the average over 25 realizations, and the full lines represent the 1σ dispersion around the mean. The synthetic Δ-variance spectra are compared to that of the Cygnus-X North region and that of an fBm image with β = 2.4.