Top: number density of cluster and group UDGs (grey band and black lines) as a function of halo mass. The horizontal green band and line indicates the number density of HUDs assuming a uniform distribution across halo mass 10¹⁰ < M₂₀₀∕M_⊙ < 10^11.5. Bottom: cumulative number density of cluster and group UDGs (grey band and black lines) in halos above a given mass. The total number density of HUDs (horizontal green band and line) is shown forcomparison. The central lines and the widths of the bands indicate the central value and 1 − σ uncertainties, respectively. The dashed black lines indicate the region over which the halo mass–UDG number relation has been extrapolated.