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Fig. 3


UVM2UVW1 versus UVW2UVM2 diagram. The colours of the circles refer to the adopted classification of the objects, based on combining the photometric classifications provided by the COMBO-17 survey and the Chandra 4 Ms source catalogue (see Sect. 3.2). Blue triangles indicate the galaxies, stars are represented as black filled circles, white dwarfs as asterisks, red filled squares indicate the AGN, while green filled circles represent the intermediate objects as defined in Sect. 3.2 (e.g. faint AGN optically diluted by the host galaxy starlight). Black empty circles refer to the sources whose classification is uncertain or unclassified. Symbols are also reported in a legend. The background black dot distribution is the whole XMM-SUSS diagram of Page et al. (2012). The most crowded region in the centre of the colour–colour plot is magnified in the small inset.

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