(i − K_S) versus (g − i) colour-colour diagram showing the Hβ+[OIII]λ4959,5007 (filled circles) and [OII]λ3726,3729 (filled diamonds) emission-line candidates at z ∼ 0.9 and 1.4, respectively, selected as explained in the text. The grey background grid represents the OTELO sources and the open circles represent those sources detected with MIPS 24 μm. As a reference, the blue line represents a colour sequence of selected galaxy templates, described in Sect. 5.5, from E/S0 type to SB1 (open squares) at redshift z  = 1.15 and E(B − V) = 0. The reddest segment of this sequence is concurrent with the intrinsic attenuation axis.