Luminosity at the synchrotron peak, L_peak, as a function of the synchrotron peak frequency value, ν_peak. The data (grey points) were extracted from the BZ Catalogue (Massaro et al. 2015). Detected sources (BL Lac, RG and FSRQ) in the HEGS FoV are given by green hexagons, purple squares, and a red dot, constrained sources (see Sect. 4.2.1) by blue triangles, and not constrained source by orange dots. For the constrained sources, 1 object do not have an entry in the BZ Catalogue: PMN J0039-2220.