AllWISE 3.4–4.6 µm brightness vs. 4.6–12 µm brightness. All values are given in Vega magnitudes. Black and red dots represent HS/N and LS/N sources, respectively. The green, cyan, and blue dashed lines illustrate the AGN-selection criteria from Stern et al. (2012), Jarrett et al. (2011), and Mateos et al. (2012), respectively. The grey dashed lines divide the diagram into regions where AGN, spheroids, intermediate disc galaxies, and star-forming galaxies are positioned following the criteria in Jarrett et al. (2017).