Time filter

Source Type

Diego J.M.,Institute Fisica Of Cantabria Uc Csic | Broadhurst T.,University of the Basque Country | Broadhurst T.,Ikerbasque | Benitez N.,Institute Astrofisica Of Andalucia Csic | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We examine Abell 1689 non-parametrically, combining strongly lensed Hubble Space Telescope images and weak distortions from wider field Subaru imaging. Our model incorporates member galaxies to improve the lens solution. By adding luminosity-scaled member galaxy deflections to our smooth grid, we can derive meaningful solutions with sufficient accuracy to permit the identification of our own strongly lensed images, so our model becomes self-consistent. We identify 11 new multiply lensed system candidates and clarify previously ambiguous cases, in the deepest optical and near-infrared data to date from Hubble and Subaru. Our improved spatial resolution brings up new features not seen when the weak and strong lensing effects are used separately, including clumps and filamentary dark matter around the main halo. Our treatment means we can obtain an objective mass ratio between the cluster and galaxy components. We find a typical mass-to-light ratios of M/LB = 21 ± 14 inside the r < 1 arcmin region. Our model independence means we can objectively evaluate the competitiveness of stacking cluster lenses for defining the geometric lensing-distance-redshift relation in a model-independent way. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Covone G.,University of Naples Federico II | Covone G.,Compl University Monte gelo | Sereno M.,University of Bologna | Kilbinger M.,SAP | Cardone V.F.,I.N.A.F. Osservatorio Astronomico di Rome
Astrophysical Journal Letters | Year: 2014

We present observational evidence of the two-halo term in the stacked shear profile of a sample of ∼1200 optically selected galaxy clusters based on imaging data and the public shear catalog from the CFHTLenS. We find that the halo bias, a measure of the correlated distribution of matter around galaxy clusters, has amplitude and correlation with galaxy cluster mass in very good agreement with the predictions based on the LCDM standard cosmological model. The mass-concentration relation is flat but higher than theoretical predictions. We also confirm the close scaling relation between the optical richness of galaxy clusters and their mass. © 2014. The American Astronomical Society. All rights reserved. Source

Cao S.,Beijing Normal University | Cao S.,University of Naples Federico II | Covone G.,University of Naples Federico II | Covone G.,Compl University Monte gelo | Zhu Z.-H.,Beijing Normal University
Astrophysical Journal | Year: 2012

We study the redshift distribution of two samples of early-type gravitational lenses, extracted from a larger collection of 122 systems, to constrain the cosmological constant in the ΛCDM model and the parameters of a set of alternative dark energy models (XCDM, Dvali-Gabadadze-Porrati, and Ricci dark energy models), in a spatially flat universe. The likelihood is maximized for ΩΛ = 0.70 ± 0.09 when considering the sample excluding the Sloan Lens ACS systems (known to be biased toward large image-separation lenses) and no-evolution, and ΩΛ = 0.81 ± 0.05 when limiting to gravitational lenses with image separation Δθ > 2″ and no-evolution. In both cases, results accounting for galaxy evolution are consistent within 1σ. The present test supports the accelerated expansion, by excluding the null hypothesis (i.e., ΩΛ = 0) at more than 4σ, regardless of the chosen sample and assumptions on the galaxy evolution. A comparison between competitive world models is performed by means of the Bayesian information criterion. This shows that the simplest cosmological constant model - that has only one free parameter - is still preferred by the available data on the redshift distribution of gravitational lenses. We perform an analysis of the possible systematic effects, finding that the systematic errors due to sample incompleteness, galaxy evolution, and model uncertainties approximately equal the statistical errors, with present-day data. We find that the largest sources of systemic errors are the dynamical normalization and the high-velocity cutoff factor, followed by the faint-end slope of the velocity dispersion function. © 2012 The American Astronomical Society. All rights reserved. Source

Capozziello S.,University of Naples Federico II | Capozziello S.,Compl University Monte gelo | Izzo L.,University of Naples Federico II | Izzo L.,University of Rome La Sapienza
Astronomy and Astrophysics | Year: 2010

Aims. The Amati relation, which connects the isotropic energy emitted and the rest-frame peak energy of the νFν spectra of GRBs, is cosmology-dependent, so we need a method to obtain an independent calibration of the Amati relation. Methods. Using the Union Supernovae Ia catalog, we obtain a cosmographic luminosity distance in the y-redshift and verify that this parameterization very well approximates the fiducial standard cosmological model ΔCDM. Using this cosmographic luminosity distance dl, we compute the Amati relation considering this cosmology-independent definition of dl. Results. The cosmographic Amati relation we obtain agrees in the errors with other cosmology-independent calibrations proposed in the literature. © 2010 ESO. Source

Capozziello S.,University of Naples Federico II | Capozziello S.,Compl University Monte gelo | Vignolo S.,University of Genoa
International Journal of Geometric Methods in Modern Physics | Year: 2012

We review the Cauchy problem for f(R) theories of gravity, in metric and metric-affine formulations, pointing out analogies and differences with respect to General Relativity. The role of conformal transformations, effective scalar fields and sources in the field equations is discussed in view of the well-formulation and the well-position of the problem. Finally, criteria of viability of the f(R)-models are considered according to the various matter fields acting as sources. © 2012 World Scientific Publishing Company. Source

Discover hidden collaborations