Comparison between the two-dimensional column densities and the three-dimensional number densities of O VII. Left: column densities of O VII projected through a 20 Mpc deep slice along the x-axis. The colour scheme indicates the O VII column density with a lower limit at log N_O VII(cm⁻²) = 15, while the Bisous filaments and high LD Bisous filaments are shown by grey and white areas, respectively. This image is the same as the middle-right panel of the column density maps in Fig. 9. The red square corresponds to the volume shown in the right-hand figure. Right: three-dimensional visualisation of the O VII distribution in a (20 Mpc)³ zoom-in box within the larger EAGLE volume. The coloured regions represent the O VII density contours at given values, as indicated on the right vertical axis. The green contour shows the spatial extent of O VII above the optimistic detection limit of n_O VII = 10⁻⁹ cm⁻³ discussed in the text. The white lines show the Bisous filament spines, while the white circles indicate the volumes within R₂₀₀ around the central galaxies of the FoF haloes. A three-dimensional visualisation is available as an online movie.