Optical appearance of the galaxy cluster XMMU J1230.3+1339 at z = 0.975. Top left: co-added 9.5′  ×  9.5′ i′z′ image showing the cluster environment. The dashed circles represent the projected cluster radii R₂₀₀ (outer) and R₅₀₀ (inner), the physical angular scale at the cluster redshift is given in the upper right corner, and the Virgo galaxy NGC 4477 is marked by the dashed circle on the right. Top right: RGB color composite based on the co-added LBT images in i′z′ (red channel), Vr′ (green), and UB (blue). The side length of the image corresponds to a physical scale of 2 Mpc  ×  2 Mpc (250″  ×  250″), displaying approximately the region inside R₂₀₀. The large number of red cluster galaxies are easily visible. Bottom left: core region of the cluster in i′z′ with Chandra X-ray contours overlaid in cyan and a side length of 560 kpc (70″); the green dashed circle marks the BCG to the South-West of the nominal X-ray center (green cross). Bottom right: same sky region as on the left as color composite.