tokens: 3 arcmin, and a zoom-in of a 45 arcsec region for closer inspection. The generated image is reasonably convincing as an extragalactic deep field from the point of view of cursory visual inspection, although like many GAN-generated images, on closer inspection there are artefacts (such as low surface brightness features, pixelization, and discontinuities not seen in the real image) that betray the counterfeit. These artefacts are likely caused by a lack of resolution in the GAN generator, and could be remedied through the addition of more layers, or through the use of a larger convolutional kernel. Both of these approaches would increase the receptive field. The GAN also cannot reproduce some of the larger galaxies with the same level of detail as the real image. Nevertheless, the generated image does contains a mixture of early- and late-type galaxies amongst a more numerous field of background sources. The early and late types have the correct colour and morphology, i.e. classic red/elliptical and blue/spiral, respectively, and background sources have the clumpy and disturbed morphology typically seen in the high-redshift galaxy population. Fig. 3 presents single-band ( F 775 W ) thumbnail images of a sample of 100 randomly chosen sources with F 775 W AB magnitudes in the range 21–26 mag. 50 sources are selected from the real image and 50 are selected from the generated images, but the thumbnails have been randomly shuffled in the figure to demonstrate to the reader the visual similarity of individual galaxies in the generated and real data. Figure 2. Example of a generated deep field. The top left panel shows a generated deep field with the RGB channels corresponding to the F 814 W , F 775 W , and F 606 W bands. The size of the generated image was set to 3.2 arcmin, spanning the full XDF (top right), which has a 60 mas pixel −1 scale. The lower panels show 45 arcsec zoom-ins of the generated and real fields. Figure 3. Thumbnail images of real and generated ‘galaxies’. Each image is 7.2 arcsec across and shows the F 775 W channel on an identical linear grey-scale for 100 sources selected in the range 21–26 mag. 50 targets are selected from each of the real and generated catalogues and displayed in random order in row-wise ascending order of magnitude. To test whether the similarity between the generated and real image is more than superficial, we extract ‘galaxies’ from the generated images and compare to those in the real XDF. We use the source finder sextractor (Bertin Arnouts 1996 ) to detect galaxies in the combined F 606 W + F 775 W + F 814 W (pixelwise-mean) images, measuring the corresponding source flux in the individual bands. Sources are identified with the criteria that five contiguous pixels have a signal ≥5σ above the local background. The same detection procedure is applied to the real and generated images, and the photometric zero-points for the generated images are identical to the real data. Fig. 4 compares the magnitude
ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O B-Wavelength I-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O B-CelestialRegion O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialRegion O O O O O B-Software B-Citation I-Citation I-Citation O O O O O O O B-Wavelength I-Wavelength I-Wavelength O B-Wavelength I-Wavelength I-Wavelength O B-Wavelength I-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O