Distribution of the full sample of galaxies in the four set of properties used to select the candidates to AGNs employed in this study: Top-left panel: X-ray properties, showing the X-ray hardness ratio as a function of the X-ray luminosity. Top-right panel: IR properties, showing the WISE W1 − W2 color as a function of the WISE W2 magnitude. Bottom-left panel: UV-optical properties, showing NUV − u color as a function of u − g one. Bottom-right panel: Radio properties, showing the ratio between the integrated and peak intensity at 1.4 GHz as a function of the integrated intensity. Each panel adopts the same symbols and color scheme: (i) solid circles correspond to the full sample of galaxies with measured properties, comprising 1390 objects for the X-ray panel, 541 478 for the IR one, 547 928 for the UV-optical one, and 15 839 for the radio one; (ii) contours represent the area that encircles 95% of the objects with ionization classified as star-forming (SFGs, blue), retired galaxies (RGs, red), and AGNs (purple) using out final classification scheme described in Sect. 3; (iii) dashed-lines show the demarcation lines described in Sect. 3 to select the AGN candidates using the represented properties.