A new (2+1)D cluster finding algorithm based on photometric redshifts:   large scale structure in the Chandra Deep Field South
  Aims: We study galaxy clustering and explore the dependence of galaxy properties on the the environment up to a redshift z~1, on the basis of a deep multi-band survey in the Chandra Deep Field South.   Methods: We have developed a new method which combines galaxy angular positions and photometric redshifts to estimate the local galaxy number-density. This allows both the detection of overdensities in the galaxy distribution and the study of the properties of the galaxy population as a function of the environmental density.   Results: We detect two moderate overdensities at z~0.7 and z~1 previously identified spectroscopically. We find that the fraction of red galaxies within each structure increases with volume density, extending to z~1 previous results. We measure ``red sequence'' slopes consistent with the values found in X-ray selected clusters, supporting the notion that the mass-metallicity relation hold constant up to z~1.   Conclusions: Our method based on photometric redshifts allows to extend structure detection and density estimates up to the limits of photometric surveys, i.e.considerably deeper than spectroscopic surveys. Since X-ray cluster detection at high redshift is presently limited to massive relaxed structures, galaxy volume density based on photometric redshift appears as a valuable tool in the study of galaxy evolution. 
Dario Trevese, Marco Castellano, Adriano Fontana and Emanuele   Giallongo