Comparison between the different properties of the C IV emission line profile. Top: relation between centroid velocity at 1/2 intensity (c(1/2)) and rest-frame equivalent width of C IVλ1549. Bottom: FWHM of C IVλ1549 versus W(C IV). Colour scheme for our sample is the same as in Fig. 4. Filled magenta squares indicate data from Martínez-Aldama et al. (2018). Blue and red open squares represent Pop. A and Pop. B HE sources from S17. Low-z FOS data from S07 are represented by grey (Pop. A) and orange (Pop. B) squares. Green point-dashed lines indicate the linear regression obtained through the bisector method including only the Pop. A sources from the four samples. Error bars refer to 1σ level of confidence and were estimated only for our sample.