Hard (0.5–7.0 keV) band image of the center of the field (a box of 460 × 240 arcsec) with the X-ray-emitting protocluster members marked with blue circles, and all the other spectroscopically confirmed protocluster members (2.0 < z < 2.3) marked with red circles. The image has been smoothed with a 1 arcsec Gaussian filter for clarity. X-ray members are labeled with the source ID, the original selection: Ha, Lya, ERO, and CO for H_α, Ly_α, red color, and CO-line selection, respectively, and “spec” for spectroscopic selection. Finally, the sources labeled with “X” were previously identified as X-ray sources in the literature, as described in Sect. 2.2.