Distribution function for C iv-enriched H i lines for Δv_C iv = ±100 km s^-1 (red filled squares) and for Δv_C iv = ±10 km s^-1 (blue stars) at 1.9 < z < 3.2. Also shown is the differential column density distribution function for all H i Lyα absorbers excluding Q0055−269 and J2233−606 (black filled circles) in the same redshift range analysed for the C iv-enriched forest. The solid line indicates the fit to filled circles for log  N_H i = [12.75,14.0]: log  dN/(dN_H idX) = (7.43 ± 0.44) + (−1.44 ± 0.03) × log  N_H i. The vertical errors indicate 1σ Poisson errors, while the x-axis error bars show the N_H i range covered by each data point. All the grey data points indicate that the data are incomplete at log  N_H i < 12.75.