α_ox versus L_{250 nm} diagram. Blue triangles and upper limits represent galaxies, red squares indicate AGN, green circles and upper limits refer to intermediate sources, and black downward arrows represent the upper limits of the Chandra undetected sources. AGN and intermediate sources are marked by small black circles when referring to their nuclear luminosities. All these symbols are also shown in the legend. Green symbols without the black circles refer to the total luminosities of intermediate sources for which it was not possible to determine the nuclear components; a correction performed as in Vagnetti et al. (2013) would shift such sources in the upper left direction with slope ~0.38. For some of the intermediate sources, black upward vertical arrows indicate the correction for the X-ray absorption based on the available X-ray spectra from the XMM-CDFS Deep Survey. The straight lines refer to the best fit α_ox − L_{250 nm} relations by Just et al. (2007; continuous) and Lusso et al. (2010; dotted) for AGN, as reference.