Fig. 2 Fig. 3 Fig. 4 The dependence of galaxy evolution on the properties of the environment, i.e. the deviation from the average behaviour, can be detected in clusters and local overdensities (Carlberg et al. 2001, Gomez et al. 2003, Ilbert et al 2006). A measure of galaxy volume-density, at the highest redshifts allowed by deep photometric surveys, to detect clusters and relate the properties of galaxy population with the environmental density, is a key step to understand galaxy formation/evolution. We show here that the accuracy provided by high quality photometric redshifts based on multi-band photometry (reaching an accuracy  z = (z spe -z phot )/(1+z spe )= 0.02 for 0 < z < 2), albeit much lower with respect to spectroscopic redshifts z spe,, may be sufficient for the statistical identification of large-scale structures. We apply this technique to a subarea of the Chandra Deep Field South (CDFS) and discuss the properties of the Red Sequence in two detected structures. Figure 2) shows the distribution of rest-frame B-R galaxy colours in two regions of density :  > 0.08 gal/Mpc 3 (shaded) and  The red galaxy fraction as a function of local density The red sequence is clearly visible in the two overdensities at z=0.7 and z=1.0. A rest- frame U-B vs. B diagram for the former is shown in Figure 4. After selecting galaxies with an environmental density above a  10 =0.08 gal/Mpc -3., we isolated the red population from the colour histograms. From this sample we measured the slope of the red- sequence in the rest-frame colour-magnitude plane. It turns out to be consistent, within 1  with the average value found by Blakeslee et al. 2003, in high z, X-ray selected clusters. Figure 5, adapted from the above paper with the inclusion of our points, supports the notion that the red-sequence slope holds constant from z=0 up to at least z=1. According to the standard interpretation this implies that the mass-metallicity relation maintains unchanged in the same redshift interval. It should be noted that, as soon as deeper (I AB ~ 27) surveys will become available (Grazian et al. 2006) it will be possible to extend the results to z~1.5 Properties of the red sequence - The application of our (2+1)D algorithm, based on photometric redshifts, allowed the detection of two overdensities at z=0.70 and z=1.0 in galaxy distribution of the CDFS, whose previous evidence was based on spectroscopy of X-ray selected sources and on sparse spectroscopic follow-up of incomplete samples in the CDFS. - The fraction of red galaxies in the two structures shows a clear increase with density, extending to z~1 previous results limited to z<0.5 - Besides confirming the physical reality of the detected structures, the colour-density relation at z~1 provides new constraints for models of galaxy evolution. - Our measurement of the slope of the colour-magnitude relation in these clusters adds a new evidence against changes of the relation between galaxy masses and their average metallicity, at least up to z~1. Conclusions Dario Trevese 1, Marco Castellano 1, Adriano Fontana 2, Emanuele Giallongo 2 1 Dipartimento di Fisica, Università di Roma “ La Sapienza”, P.le A. Moro 2, Roma 2 INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, Monte Porzio Catone The increase of the fraction of red galaxies for increasing density is shown in figures 3 for the two overdensities at z=0.7 (left), z=1.0 (right). The slope of the red-fraction vs. density relation is consistent in the two overdensities. Environmental effects on galaxy evolution in the Chandra Deep Field South Clusters in the CDFS A 6.4x6.1 arcmin field in the Chandra Deep Field South (CDFS) with UBVRIZJK bands photometry (Cimatti et al. 2OO2), limited to I AB <25 has been analysed. We have constructed (2+1)D maps of the volume density  N, with N=10. Three main clumps appear about redshift 0.70, 0.95 and We adopted density threshold  10 =0.08 Mpc -3, above which 0.02% of the total number of cells is found. The presence of the first two structures was indicated by the distribution of spectroscopic resdshifts of X-ray selected sources in the field (Gilli et al. 2003). From our analisys of the galaxy distribution these overdensity correspond to clusters of richness class 0. Figure 1 shows the distribution of photometric redshifts of the sample and the average density  n density on the entire field. Fig. 5 Fig. 1 A (2+1)D cluster finding algorithm for photometric surveys Galaxy types distribution: average versus local We have developed a new algorithm (Trevese et al. 2006) to compute a three dimensional galaxy density, which we call (2+1)D to remind that the positional accuracy along the line of sight is much lower than the angular one. Yet all the available positional information is taken into account simultaneously. The ( , ,z) space is divided in cells whose size in each direction depends on the relevant positional uncertainty, thus they are elongated in the radial direction. Objects are counted in increasing volumes V around each cell, until a fixed number N is reached and a density  =N/V(gal/Mpc 3 ) is assigned to the cell. The number N is chosen to be of the order of the number of galaxies present in a single cell located in a region of high galaxy density. The increasing loss of faint galaxies at high redshift, due to the survey limiting magnitude, is taken into account by assigning to each object a weight depending on the average luminosity function. Clusters or groups are defined as connected regions with density exceeding a fixed threshold. The distribution of galactic types can by analysed as a function of the density  of the local environment. REFERENCES Blakeslee, J.P. et al. 2003, AJ 596, L143 Carlberg et al., 2001, ApJ 563, 736 Cimatti, A. et al. 2002, A&A 381L, 68 Giallongo, E. et al. 2005, ApJ 622, 116 Gomez, P.L. et al. 2003, ApJ, 584, 210 Grazian, A. et al in press, astro- ph/ Ilbert, O. et al. 2006, astro-ph/ Menci, N. et al 2005, ApJ 632, 49 Trevese, Castellano, Fontana, Giallongo 2006 (subm) Fig. 2