Coloured points: r − W1 colour vs. redshift for all our candidates with a counterpart in WISE. Our sources are uniformly spread within the z interval sampled by each NB. Grey lines: tracks for different galaxy templates (from the SWIRE library, Polletta et al. 2007) and the QSO template of Hernán-Caballero et al. (2016). Black-contoured and yellow-contoured points mark the SDSS QSOs in our selection and the GTC targets (only for J0395 NB), respectively. Our candidates are all compatible with the high-z QSO template, suggesting that the fraction of SF LAEs in our sample is very low. In addition, this suggests that we identify a large number of sources without previous spectroscopic identification as high-z QSOs.