Showing papers by "Giovanni Covone published in 2005"
TL;DR: In this article, Chandra, XMM-Newton, HST and ARC observations of an extended X-ray source at z = 0.59 were used to construct a high redshift fossil group.
Abstract: This is a report of Chandra, XMM-Newton, HST and ARC observations of an extended X-ray source at z = 0.59. The apparent member galaxies range from spiral to elliptical and are all relatively red (i\'-Ks about 3). We interpret this object to be a fossil group based on the difference between the brightness of the first and second brightest cluster members in the i\'-band, and because the rest-frame bolometric X-ray luminosity is about 9.2x10^43 h70^-2 erg s^-1. This makes Cl 1205+44 the highest redshift fossil group yet reported. The system also contains a central double-lobed radio galaxy which appears to be growing via the accretion of smaller galaxies. We discuss the formation and evolution of fossil groups in light of the high redshift of Cl 1205+44.
44 citations
TL;DR: In this article, a friend-of-friend based algorithm applied to the spectroscopic redshift catalog and an adaptative kernel galaxy density and colour maps correlated with photometric redshift estimates have been used.
Abstract: We have used the Vimos VLT Deep Survey in combination with other spectroscopic, photometric and X-ray surveys from literature to detect several galaxy structures in the Chandra Deep Field South (CDFS). Both a friend-of-friend based algorithm applied to the spectroscopic redshift catalog and an adaptative kernel galaxy density and colour maps correlated with photometric redshift estimates have been used. We mainly detect a chain-like structure at z=0.66 and two massive groups at z=0.735 and 1.098 showing signs of ongoing collapse. We also detect two galaxy walls at z=0.66 and at z=0.735 (extremely compact in redshift space). The first one contains the chain-like structure and the last one contains in its center one of the two massive groups. Finally, other galaxy structures that are probably loose low mass groups are detected. We compare the group galaxy population with simulations in order to assess the richness of these structures and we study their galaxy morphological contents. The higher redshift structures appear to probably have lower velocity dispersion than the nearby ones. The number of moderatly massive structures we detect is consistent with what is expected for an LCDM model, but a larger sample is required to put significant cosmological constraints.
37 citations
TL;DR: In this paper, the photometric plane (PHP) relation between the effective radius re, the mean surface brightness within that radius e, and the Sersic index n, in optical (R and I) and near-infrared (K) bands for a large sample of early-type galaxies (ETGs) in the rich cluster MS1008-1224 at z=0306.
Abstract: We study the Photometric Plane (PHP), namely the relation between the effective radius re, the mean surface brightness within that radius e, and the Sersic index n, in optical (R and I) and near-infrared (K) bands for a large sample of early-type galaxies (ETGs) in the rich cluster MS1008-1224 at z=0306 The PHP relation has an intrinsic dispersion of ~32% in re, and turns out to be independent of waveband This result is consistent with the fact that internal colour gradients of ETGs can have only a mild dependence on galaxy luminosity (mass) There is no evidence for a significant curvature in the PHP We show that this can be explained if this relation origins from a systematic variation of the specific entropy of ETGs along the galaxy sequence, as was suggested from previous works The intrinsic scatter of the PHP is significantly smaller than for other purely photometric relations, such as the Kormendy relation and the photometric Fundamental Plane, which is constructed by using colours in place of velocity dispersions The scatter does not depend on the waveband and the residuals about the plane do not correlate with residuals of the colour-magnitude relation Finally, we compare the coefficients of the PHP at z~03 with those of ETGs at z~0, showing that the PHP is a valuable tool to constrain the luminosity evolution of ETGs with redshift The slopes of the PHP do not change significantly with redshift, while the zero-point is consistent with cosmological dimming of the surface brightness in an expanding universe plus the passive fading of galaxy stellar populations with a high formation redshift (z_f >1-2)
20 citations
TL;DR: In this article, the effect of small-scale inhomogeneities on large-scale observations within the statistics of gravitationally lensed quasars is evaluated. But the authors consider a cosmological model whose large scale properties (dynamics, matter distribution) are the same as in Friedmann-Lemaˆ itre models, but whose matter distribution is locally inhomogeneous.
Abstract: We evaluate the effect of small-scale inhomogeneities on large-scale observations within the statistics of gravitationally lensed quasars. To this end, we consider a cosmological model whose large-scale properties (dynamics, matter distribution) are the same as in Friedmann- Lemaˆ itre models, but whose matter distribution is locally inhomogeneous. We use the well- known Dyer-Roder distances to allow a simple analytical expression of the optical depth τ , and pay particular attention to the different roles played by the different notions of distance (filled beam angular diameter distance and Dyer-Roder distances) when calculating this quantity, following the 1986 prescription of Ehlers & Schneider for a coherent formalism. We find that the expected number of gravitationally lensed quasars is a decreasing function of the clumpiness parameter α. Ke yw ords: gravitational lensing - cosmological parameters - cosmology: observations.
9 citations
TL;DR: In this paper, the authors presented extensive multi-color imaging and low-resolution VIMOS Integral Field Unit spectroscopic observations of the X-ray luminous cluster Abell 2667 (z=0.233).
Abstract: (abridged) We present extensive multi-color imaging and low resolution VIMOS Integral Field Unit spectroscopic observations of the X-ray luminous cluster Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is easily identified as part of a triple image system and other fainter multiple images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations cover a field of view of 54'' x 54'' and enable us to determine the redshift of all galaxies down to V=22.5. Furthermore, redshifts could be identified for some sources down to V=23.2. In particular we identify 21 cluster members in the cluster inner region, from which we derive a velocity dispersion of \sigma=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses within a 110 kpc radius. Using the multiple images constraints and priors on the mass distribution of cluster galaxy halos we construct a detailed lensing mass model leading to a total mass of 2.9 x 10^{13} solar masses within the Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good agreement although the dynamical one is much less accurate. Comparing these measurements with published X-ray analysis, is however less conclusive. Although the X-ray temperature matches the dynamical and lensing estimates, the published NFW mass model derived from the X-ray measurement with its small concentration of c ~3 can not account for the large Einstein radius observed in this cluster. A larger concentration of ~6 would however match the strong lensing measurements. These results are likely reflecting the complex structure of the cluster mass distribution, underlying the importance of panchromatic studies from small to large scale in order to better understand cluster physics.