Projected phase space for the galaxies in SPT0311–58. The x-axis is the projected distance from the cluster centre in units of R₂₀₀. The y-axis shows the absolute value of the relative velocity along the line of sight of each galaxy with respect to the global recessional velocity, normalised by the velocity dispersion of the cluster. The red dots correspond to a global cluster redshift of z_sys = 6.902 as inferred for the W galaxy from the [CII] line, and the green dots are for an ad-hoc z_sys = 6.912. The blue line represents the escape velocity normalised by the velocity dispersion of the cluster for a Navarro, Frenk, and White dark matter halo (Navarro et al. 1996) of M₂₀₀ = 5 ×  10¹² M_⊙, with the blue shadow defining the region for masses between 2 and 8 × 10¹² M_⊙. The point for the W galaxy at (0, 0) has been slightly shifted to make it more visible.