Observed (u − r) colour versus morphological parameters for all the sources of OTELO. From left to right: logarithm of the Sérsic index in the filter F814W (I), concentration index for the I filter too, and the logarithm of the wavelength-dependent ratio of the Sérsic indices for I and V (F606W). Triangles and solid lines in grey (histograms) represent LT, squares and dashed lines in black (histograms) represent ET galaxies. Red circles represent the [O II]3727 emitters from our sample with HST/ACS ancillary data. Top histograms corresponds to the respective value, as indicated in x-axis label, while right-hand histogram show (u − r) distribution. All histograms represents density distributions. Horizontal dot-dashed line in black shows (u − r) = 2.5. Red dashed line shows the results from de Diego et al. (2020). Dashed lines in magenta represent limits from Vika et al. (2015): horizontal cut in (u − r) = 2.3, while vertical dashed-lines in magenta represent log(n_I) = 0.4 and . Figure adapted from Nadolny et al. (2021).