V_max computation scheme for a galaxy from the main-ELG sample (star symbol). Top panel: we take into account the survey r-band magnitude limit ; note that we are omitting the K-corrections (K(z_i) = 0 in Eq. (8)) for this representation. Bottom panel: similar plot as the top one for a survey with a limit in the Hα line flux of . For the [O II], [O III], Hβ, [N II], and [S II] lines the methodology is identical (see Sect. 2.3). The lower and upper redshift limits of the survey, z_low = 0.02 and z_up = 0.22, are highlighted by dashed vertical red lines in both panels. The maximum redshifts that the galaxy can have and still be included in the sample, considering its magnitude and Hα flux limits, as well as the faintest luminosity, are shown by dotted vertical blue lines.