Tracing the Large‐Scale Structure in theChandraDeep Field South

We report the discovery of large scale structures of X-ray sources in the1Msec observation of the Chandra Deep Field South. Two main structures appearas narrow (Delta_z < 0.02) spikes in the source redshift distribution at z=0.67and z=0.73, respectively. Their angular distribution spans a region at least ~17 arcmin wide, corresponding to a physical size of 7.3 h_{70}^{-1} Mpc at aredshift of z ~ 0.7 (Omega_m=0.3, Omega_{Lambda}=0.7). These spikes arepopulated by 19 sources each, which are mainly identified as Active GalacticNuclei (AGN). Two sources in each spike are extended in X-rays, correspondingto galaxy groups/clusters embedded in larger structures. The X-ray sourceredshift distribution shows other spikes, the most remarkable at z=1.04, 1.62and 2.57. This is one of the first evidences for large scale structure tracedby X-ray sources and for spatial clustering of X-ray selected AGN. The X-raydata have been complemented with the spectroscopic data from the K20 nearinfrared 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. Twonarrow structures at z=0.67 and z=0.73 (again with Delta_z ~ 0.02) are the mostsignificant features, containing 24 and 47 galaxies, respectively. While theK20 structure at z=0.73 is dominated by a standard galaxy cluster with asignificant concentration around a central cD galaxy and morphologicalsegregation, the galaxies at z=0.67 constitute a loose structure ratheruniformly distributed along the K20 field.[abridged]