Mass-redshift sampling in the ECDF-S. Definition of mass is done with respect to the mean density and is scaled by the Hubble constant. Grey shadowing indicate the density of detected groups in simulations, with Planck cosmological parameters (Planck Collaboration XXVI 2014) and the scaling relations of Leauthaud et al. (2010) used. Solid circles show the parameters of ECDF-S groups. The dashed and solid lines show the location of 90% and 50% detection completeness level.