ΣSFR/richness (in units of M_⊙   yr^-1) as a function of the average r-band galaxy density within each region. Richnesses and densities are estimated using galaxies brighter than 7 × 10⁹   L_⊙ in the r-band. Different symbols identify the three different regions, as in Fig. 12, and the filled black diamond identifies the region within R ≤ 0.5   r₂₀₀. 1σ error bars are shown. The dashed line represents the expected value at the cluster mean z, using the relation of Bai et al. (2009) between ΣSFR/mass and z, and the richness/mass value of the A1763 virial (R ≤ r₂₀₀) region (see Sect. 3.4).