AB magnitude in the r band of all the 243 extragalactic sources in the Chandra J1030 sample with an optical and/or NIR counterpart (solid black line), the 123 sources with spectroscopic redshift (dashed red line), the 120 sources with only photometric redshift (dotted blue line) and the 43 BL–AGNs (solid yellow line). We assign to the 24 sources with no r-band detection a magnitude r_AB = 27.5, which is their upper limit. The BL–AGN with an r-band upper limit at r_aB = 27.5 is the z = 6.3 QSO SDSSJ1030+0525.