Expected number densities for photometric and spectroscopic emission line flux selected samples as a function of redshift in the Euclid Wide Survey. Different colours show various selection cuts for the EWS (in I_E , H_E , and in the 2 model calibrations for the line fluxes of f_Hα+[N II] > 2 × 10⁻¹⁶ erg s⁻¹ cm⁻²). The empirical model of Pozzetti et al. (2016) and the data based on slitless HST spectroscopy (Bagley et al. 2020) are also shown.