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tokens: to CMB observations at a frequency around 150 GHz and shows a high level of non-Gaussianity in both total intensity and polarization. We therefore choose to apply our algorithm to thermal dust maps, with the goal of obtaining simulations with realistic and nontrivial small-scale structures at subdegree angular resolution. In this section, we describe the methodology used as well as the results obtained. Existing templates of thermal dust emission on the full sky have been obtained by applying component separation algorithms to Planck maps. In this work, we used the ones obtained using the GNILC (Generalized Needlet Internal Linear Combination) method at 353 GHz, which have the advantage of not being contaminated by CIB radiation in total intensity (for a detailed description of the data and the method applied to get this thermal dust template, we refer to Planck Collaboration Int. XLVIII 2016 ). The GNILC dust maps have an angular resolution that varies in the sky and depends on the S/N of the Planck high-frequency maps: in total intensity, the effective beam FWHM ranges from 5′ to about 22′, while in polarization, it varies in the interval 5′–80′ (Planck Collaboration IV 2020 ). 10 10 The GNILC maps are available on the Planck Legacy Archive website, http://pla.esac.esa.int/pla/#maps . Both polarization and intensity maps follow the HEALPix 11 11 https://healpix.sourceforge.io/index.php pixelization scheme (Górski et al. 2005 ) at N side = 2048, i.e., ∼1.7′ pixel resolution. 4.1. Total Intensity We first tested the ability of F or SE to generate realistic small-scale features in total intensity (quantified by the Stokes I parameter). To do so, we needed a set of patches for which real small-scale structures have been observed. As stated above, the GNILC template in total intensity has a variable angular resolution, which is equal to 5′ in regions close to the Galactic plane, thus making them suitable to be used to train the GAN. In order to further select only those regions less contaminated by noise, we built a mask from the Planck HFI 353 GHz I map. In particular, we took into account only that part of the sky where the S/N in the 353 GHz map at the full angular resolution (about 5′) is above a threshold of 8. We smoothed the obtained mask with a Gaussian beam with an FWHM of 1° in order to regularize its borders. We also cut out the inner part of the Galactic plane (with b 10°), which, due to its peculiarity, is not suitable to be used as part of the training set. The resulting mask is shown in Figure 2 and covers a fraction of the sky of about 23%. Figure 2. Sky mask adopted in this work (see Section 4.1 for details). Images used to perform the GAN training have been selected within the purple region. Yellow dots represent the position of the center of the patches shown in Figures 3 – 5 , whereas the green one corresponds to the patch in Figures 6 – 8 . In order to train the GAN, both M LS and images were needed. The M LS patches