Logarithmic host galaxy column density of the highly ionised atoms C iv, Si iv, N v, and O vi against the total logarithmic column densities of C, Si, N, and O in the top, second, third, and bottom panels, respectively. The total column densities are derived from X-ray observations, denoted by N_X. The C iv, Si iv, N v, and O vi measurements plotted as circles are all taken from Fox et al. (2008), the N v data plotted as squares are from Prochaska et al. (2008), and data taken from D’Elia et al. (2010) are plotted as triangles. In all four panels, the dashed line corresponds to where the normalised soft X-ray column density is equal to the column density of the corresponding highly ionised atom.