Selection of a volume-limited cluster sample in the eRASS1 simulation. Top panel: sky map with the cluster population in areas covered by different depth. Areas 0, 1, 2, and 3 respectively cover regions with exposure larger than 0 s, 110 s, 150 s, and 400 s. They are cumulative areas with respect to the ones defined in Table 4. Bottom panels: population of simulated and detected clusters in the luminosity–redshift plane. The black dashed lines denote the chosen flux threshold at each depth (see Table 4). The red dashed lines locate different areas above the given flux limits. The volume-limited sample is constructed with the objects within the regions delimited by these lines.