Distribution of most of the 134 confirmed members of galaxy cluster J0152.7 shown on a VLT FORS1 R-band image. North is up and east is to the left. Blue squares are star-forming galaxies, red circles are passive galaxies, and purple triangles are X-ray sources. The image measures approximately 6.8 × 6.8 arcmin, or 3.12 × 3.12 proper Mpc at z = 0.84. The black circle represents the estimated virial radius of 1.4 Mpc from Demarco et al. (2005). Thick dashed and solid black lines represent the boundaries of intermediate- and high-density regions, respectively, as defined in Sect. 3.1.