EW distribution of the different spectral features. The thick black line histogram indicates only detections, whereas the dotted histogram includes also the limits. The red line is the best fit of the complete histogram with a lognormal distribution. In some cases there is a dashed blue line for the physical fit, as described in Sect. 3.4. In green we show a histogram of EWs, and its correspondent lognormal fit, of a sample of DLA systems (see Sect. 3.3) for a subsample of lines.