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We report the discovery of large scale structures of X-ray sources in the 1Msec observation of the Chandra Deep Field South. Two main structures appear as narrow (Deltaᵦ < 0. 02) spikes in the source redshift distribution at z=0. 67 and z=0. 73, respectively. Their angular distribution spans a region at least ~ 17 arcmin wide, corresponding to a physical size of 7. 3 h₇₀^-1 Mpc at a redshift of z ~ 0. 7 (Omegaₘ=0. 3, Omega₋₀₌₁₃₀=0. 7). These spikes are populated by 19 sources each, which are mainly identified as Active Galactic Nuclei (AGN). Two sources in each spike are extended in X-rays, corresponding to galaxy groups/clusters embedded in larger structures. The X-ray source redshift distribution shows other spikes, the most remarkable at z=1. 04, 1. 62 and 2. 57. This is one of the first evidences for large scale structure traced by X-ray sources and for spatial clustering of X-ray selected AGN. The X-ray data have been complemented with the spectroscopic data from the K20 near infrared survey (Cimatti et al. 2002), which covers ~1/10 of the X-ray field. Also in this survey the source redshift distribution shows several spikes. Two narrow structures at z=0. 67 and z=0. 73 (again with Deltaᵦ ~ 0. 02) are the most significant features, containing 24 and 47 galaxies, respectively. While the K20 structure at z=0. 73 is dominated by a standard galaxy cluster with a significant concentration around a central cD galaxy and morphological segregation, the galaxies at z=0. 67 constitute a loose structure rather uniformly distributed along the K20 field. abridged
Gilli et al. (Thu,) studied this question.