Centroid velocity at 1/2 flux intensity, c(1/2), for the C IVλ1549 emission line versus the FWHM of the full profile of C IV. Filled circles represent our sample and the colour scheme is the same as in Fig. 4. Blue and red open squares are high-redshift sources from S17. Low-z Pop. A and Pop. B are represented by grey and orange open squares, respectively. Dashed line represents the least squares linear regression presented in Eq. (2), including only Pop. A sources. Error bars refer to 1σ level of confidence for our sample.