Panel a: log SFR vs. log(M_⋆/M_⊙) for our entire Mg II sample (purple dots); the magnesium emitting galaxies with equivalent widths of Hβ emission lines EW(Hβ) > 200 Å and < 20 Å are emphasised by small black and red dots, respectively. Additionally, out of our entire SDSS DR14 sample of low-metallicity star-forming galaxies (∼30 000) only galaxies with EW(Hβ) > 200 Å and EW(Hβ) < 20 Å are shown by grey and green dots, respectively. We also include the observed data and extrapolations to lower masses for star-forming galaxies from Whitaker et al. (2012) [0.0 < z < 0.5] by a solid blue line and [2.0 < z < 2.5] by a solid red line. Additionally, the locations of Mg II emitters by Feltre et al. (2018) are indicated by dashed black lines and their Mg II absorbers by dashed yellow lines. Other symbols are the same as in Fig. 7. Panel b: only SDSS DR14 star-forming galaxies with EW(Hβ) > 200 Å are shown. Symbols are as in panel a.