Three-dimensional spatial distribution of galaxies in the five identified groups as well as the overdensity at z = 7.88, shown in comoving coordinates ΔRA, ΔDec, and grism redshift z. Each panel corresponds to one overdensity. Points are coloured by the best-fit neutral hydrogen column density log₁₀(N_HI): galaxies with log₁₀(N_HI) > 20 use a shared colour scale (right), while galaxies with log₁₀(N_HI)≤20 are shown in grey. A common colour bar is used for all high-N_HI values to enable direct comparison across groups. In panel (f), the two galaxies observed with the NIRSpec prism and associated with ALT sources are highlighted with diamond symbols and coloured according to their prism-based N_HI measurements. Square symbols denote additional galaxies with prism spectra that are not part of the ALT survey also coloured according to their prism-based N_HI measurements.