Expected magnitude limits in the continuum (S/N = 10) with 30–50 h integration time are shown for ELT, (orange, Evans et al. 2013), JWST (black, available in tabular form http://www.stsci.edu/jwst/instruments/nirspec/sensitivity/) and a VLT-FORS (green, this work). The estimated limit for KMOS is magnitude ≃21.5 in the YJ band with 50h integration (rescaling from the KMOS manual, Sect. 2.3.4). The schematic position of GDS_1408 is reported (blue) with the continuum magnitude ≃26.1, the typical ultraviolet absorption lines from the Lyα to CIV 1550 (grey region, UV-abs) and the basic emission lines, e.g., CIII]1909, [OII]3727, Hβ, [OIII]4959-5007 and Hα.