Piergiorgio Tozzi

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We use numerical simulations to examine the substructure within galactic and cluster mass halos that form within a hierarchical universe. Clusters are easily reproduced with a steep mass spectrum of thousands of substructure clumps that closely matches observations. However, the survival of dark matter substructure also occurs on galactic scales, leading to(More)
  • Optical Spectroscopy, G P Szokoly, J Bergeron, G Hasinger, I Lehmann, L Kewley +13 others
  • 2004
We present the results of our spectroscopic follow-up program of the X-ray sources detected in the 942 ks exposure of the Chandra Deep Field South (CDFS). 288 possible counterparts were observed at the VLT with the FORS1/FORS2 spectrographs for 251 of the 349 Chandra sources (including three additional faint X-ray sources). Spectra and R-band images are(More)
We present our first results from 130 ks of X–ray observations obtained with the Advanced CCD Imaging Spectrometer on the Chandra X–ray Observatory. The field of the two combined exposures is 0.096 square degrees and the detection limit is to a S/N ratio of 2 (corresponding to ∼ 7 net counts). We reach a flux of 2 × 10 −16 erg s −1 cm −2 in the 0.5–2 keV(More)
We analyse parallel N-body simulations of three Cold Dark Matter (CDM) universes to study the abundance and clustering of galaxy clusters. The simulation boxes are 500h −1 Mpc on a side and cover a volume comparable to that of the forthcoming Sloan Digital Sky Survey. The use of a treecode algorithm and 47 million particles allows us at the same time to(More)
A simple two color selection based on B-, z-, and K-band photometry is proposed for culling galaxies at 1.4 < ∼ z < ∼ 2.5 in K-selected samples and classifying them as star-forming or passive systems. The method is calibrated on the highly complete spectroscopic redshift database of the K20 survey, verified with simulations and tested on other datasets.(More)
OBJECTIVE The postoperative course of cyanotic children is generally more complicated than that of acyanotic children. A possible reason is reoxygenation injury at the beginning of cardiopulmonary bypass. In this study we tested the hypothesis that reoxygenation of chronically hypoxic hearts is worse than that of normoxic hearts. METHODS Two groups of(More)
We present results from Tree+SPH simulations of a galaxy cluster, aimed at studying the metal enrichment of the intra–cluster medium (ICM). The simulation code includes a fairly advanced treatment of star formation, as well as the release of energy feedback and detailed yields from both type-II and type-Ia supernovae, also accurately accounting for the(More)
Aims. We present a detailed mass reconstruction of the cluster RCS0224-0002 at z = 0.773 from the strong lensing features observed with HST/WFPC2. Methods. The mass profile is reconstructed using a parametric approach. We introduce a novel method to fit extended multiple images based on the Modified Hausdorff Distance between observed arcs and the arcs(More)
We present a study on the origin of the metallicity evolution of the intra-cluster medium (ICM) by applying a semi-analytic model of galaxy formation to N-body/SPH (smoothed particle hydrodynamic) non-radiative numerical simulations of clusters of galaxies. The semi-analytic model includes gas cooling, star formation, supernovae feedback and metal(More)
We present an analysis of 109 moderate-luminosity (41.9 ≤ log L 0.5−8.0 keV ≤ 43.7) AGN in the Extended Chandra Deep Field-South survey, which is drawn from 5,549 galaxies from the COMBO-17 and GEMS surveys having 0.4 ≤ z ≤ 1.1. These obscured or optically-weak AGN facilitate the study of their host galaxies since the AGN provide an insubstantial amount of(More)