Dependence of infall onto groups from regions with different density environments in observational data. The lines correspond to the mean infalling velocity onto groups embedded in regions with δρ_e >  4 (dot–dashed), 2 <  δρ_e <  4 (dashed), and 0 <  δρ_e <  2 (solid). The three gray shaded regions represent the variance from equivalent high-, medium-, and low-density environments in the mock catalogs, respectively. Error bars correspond to the uncertainties in the derived mean infalling velocities.