Redshift cumulative distribution function around z = 2.78 for the Chandra J1030 sources with a spectroscopic redshift (full markers), and for all the J1030 sources with a spectroscopic redshift, including the non-X-ray-detected ones (empty markers). The overall cumulative distribution function has been shifted by 0.1 for visualization purposes. The z ∼ 2.78 structure is marked with an arrow. Other two potential structures can be observed at z ∼ 2.37 and z ∼ 2.51 (see the text for more details).