Upper panel: diagram of relative line-of-sight velocity vs. projected cluster centric distance of the candidate member galaxies in S1101. Grey shadow shows the f_q(r,v) contours. The thick grey curve highlights the equal-density curve of f_q(r,v) = κ. Red circles and black diamonds indicate galaxies within and beyond r = 0.896 Mpc (used for constraining κ), respectively. The blue dashed curve refers to the estimated caustic of the cluster, hence all galaxies with their velocities beyond are excluded from the member sample in this method. Green open diamonds highlight cluster members previously known in the literature. Lower panel: mass profile of S1101. The mass profile from the caustic method (see Sect. 3.5) is shown as a blue thick curve, where the blue dashed curves show the corresponding 1σ error estimate. The grey dashed and dotted lines trace the measured positions of and for Δ = { 500,200 }, respectively, according to the caustic mass distribution. For comparison, we overplot the dynamical mass M₂₀₀ derived from the velocity dispersion according to Munari et al. (2013) as large black dot, the X-ray mass estimates M₅₀₀ (Zhang et al. 2011) and (Reiprich & Böhringer 2002) as black X and open diamond, respectively, and the SZ mass proxy as a dashed line with its lower error interval as dotted lines in magenta. Values of all mass proxies are also given in Table 2.