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Demianski M.,University of Warsaw | Demianski M.,Williams College | Piedipalumbo E.,University of Naples Federico II | Piedipalumbo E.,Compl University Monte gelo | And 3 more authors.
Astronomy and Astrophysics | Year: 2017

Context. Gamma-ray bursts (GRBs) are the most energetics explosions in the Universe. They are detectable up to very high redshifts. They may therefore be used to study the expansion rate of the Universe and to investigate the observational properties of dark energy, provided that empirical correlations between spectral and intensity properties are appropriately calibrated. Aims. We used the type Ia supernova (SN) luminosity distances to calibrate the correlation between the peak photon energy, Ep,i, and the isotropic equivalent radiated energy, Eiso in GRBs. With this correlation, we tested the reliability of applying these phenomena to measure cosmological parameters and to obtain indications on the basic properties and evolution of dark energy. Methods. Using 162 GRBs with measured redshifts and spectra as of the end of 2013, we applied a local regression technique to calibrate the Ep,i-Eiso correlation against the type Ia SN data to build a calibrated GRB Hubble diagram. We tested the possible redshift dependence of the correlation and its effect on the Hubble diagram. Finally, we used the GRB Hubble diagram to investigate the dark energy equation of state (EOS). To accomplish this, we focused on the so-called Chevalier-Polarski-Linder (CPL) parametrization of the dark energy EOS and implemented the Markov chain Monte Carlo (MCMC) method to efficiently sample the space of cosmological parameters. Results. Our analysis shows once more that the Ep,i-Eiso correlation has no significant redshift dependence. Therefore the high-redshift GRBs can be used as a cosmological tool to determine the basic cosmological parameters and to test different models of dark energy in the redshift region (), which is unexplored by the SNIa and baryonic acoustic oscillations data. Our updated calibrated Hubble diagram of GRBs provides some marginal indication (at 1σ level) of an evolving dark energy EOS. A significant enlargement of the GRB sample and improvements in the accuracy of the standardization procedure is needed to confirm or reject, in combination with forthcoming measurements of other cosmological probes, this intriguing and potentially very relevant indication. © ESO, 2017.

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.

Cardone V.F.,National institute for astrophysics | Perillo M.,University of Salerno | Perillo M.,Compl University Monte gelo | Capozziello S.,Compl University Monte gelo | Capozziello S.,University of Naples Federico II
Monthly Notices of the Royal Astronomical Society | Year: 2011

Because of their enormous energy release, which allows us to detect them up to a very high redshift, gamma-ray bursts (GRBs) have recently attracted a lot of interest with regards to probing the Hubble diagram (HD) deep into the matter-dominated era; thus, GRBs complement Type Ia supernovae (SNe Ia). However, with the lack of a local GRB sample, it is not easy to calibrate the scaling relations proposed as an equivalent to the Phillips law to standardize GRBs, because of the need to estimate the GRB luminosity distance in a model-independent way. We consider here three different calibration methods, based on the use of a fiducial ΛCDM model, on cosmographic parameters and on the local regression on SNe Ia. We find that the calibration coefficients and the intrinsic scatter do not significantly depend on the adopted calibration procedure. We then investigate the evolution of these parameters with the redshift. We find no statistically motivated improvement in the likelihood, so the no-evolution assumption is actually a well-founded working hypothesis. Under this assumption, we then consider possible systematics effects on the HDs introduced by the calibration method, the averaging procedure and the homogeneity of the sample, arguing against any significant bias. We nevertheless stress that a larger GRB sample with smaller uncertainties is needed to definitely conclude that the different systematics considered here have indeed a negligible impact on the HDs, thus strengthening the use of GRBs as cosmological tools. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Huertas-Company M.,Paris Observatory | Huertas-Company M.,University Paris Diderot | Mei S.,Paris Observatory | Mei S.,University Paris Diderot | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the dependence of the galaxy size evolution on morphology, stellar mass and largescale environment for a sample of 298 group and 384 field quiescent early-type galaxies from the COSMOS survey, selected from z1 to the present, and with masses log(M/M) 10.5. From a detailed morphological analysis we infer that 80 per cent of passive galaxies with mass log(M/M) 10.5 have an early-type morphology and that this fraction does not evolve over the last 6 Gyr. However, the relative abundance of lenticular and elliptical galaxies depends on stellarmass. Elliptical galaxies dominate only at the very high mass end - log(M/M) 11 - while S0 galaxies dominate at lower stellar masses - 10.5 log(M/M) 11. The galaxy size growth depends on galaxy mass range and early-type galaxy morphology, e.g. elliptical galaxies evolve differently than lenticular galaxies. At the low-mass end - 10.5 log(M/M) 11 - ellipticals do not show strong size growth from z 1 to the present (10 to 30 per cent depending on the morphological classification). On the other end, massive ellipticals - log(M/M) 11.2 - approximately doubled their size. Interestingly, lenticular galaxies display different behaviour: they appear more compact on average and they do show a size growth of 60 per cent since z = 1 independent of stellar mass range. We compare our results with state-of-the art semi-analytic models. While major and minor mergers can account for most of the galaxy size growth, we find that with present data and the theoretical uncertainties in the modelling we cannot state clear evidence favouring either merger or mass-loss via quasar and/or stellar winds as the primary mechanism driving the evolution. The galaxy mass-size relation and size growth do not depend on environment in the halo mass range explored in this work (field to group mass log(Mh/M) 14), i.e. group and field galaxies follow the same trends. At low redshift, where we examine both Sloan Digital Sky Survey and COSMOS groups, this result is at variance with predictions from some current hierarchical models that show a clear dependence of size growth on halo mass for massive ellipticals (log(M/M) 11.2). In future work, we will analyse in detail if this result is specific of the observations and model used in this work. Brightest Cluster Galaxies (BCG) and satellite galaxies lie on the same mass-size relation, at variance with predictions from hierarchical models, which predict that BCGs should have larger sizes than satellites because they experience more mergers in groups over the halo mass range probed. 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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.

Capozziello S.,University of Naples Federico II | Capozziello S.,Compl University Monte gelo | de Laurentis M.,University of Naples Federico II | de Laurentis M.,Compl University Monte gelo
Foundations of Physics | Year: 2010

In this review paper, we discuss how gravity and spin can be obtained as the realization of the local Conformal-Affine group of symmetry transformations. In particular, we show how gravitation is a gauge theory which can be obtained starting from some local invariance as the Poincaré local symmetry. We review previous results where the inhomogeneous connection coefficients, transforming under the Lorentz group, give rise to gravitational gauge potentials which can be used to define covariant derivatives accommodating minimal couplings of matter, gauge fields (and then spin connections). After we show, in a self-contained approach, how the tetrads and the Lorentz group can be used to induce the spacetime metric and then the Invariance Induced Gravity can be directly obtained both in holonomic and anholonomic pictures. Besides, we show how tensor valued connection forms act as auxiliary dynamical fields associated with the dilation, special conformal and deformation (shear) degrees of freedom, inherent to the bundle manifold. As a result, this allows to determine the bundle curvature of the theory and then to construct boundary topological invariants which give rise to a prototype (source free) gravitational Lagrangian. Finally, the Bianchi identities, the covariant field equations and the gauge currents are obtained determining completely the dynamics. © 2009 Springer Science+Business Media, LLC.

Capozziello S.,University of Naples Federico II | Capozziello S.,Compl University Monte gelo | Martin-Moruno P.,Institute Fisica Fundamental | Rubano C.,University of Naples Federico II | Rubano C.,Compl University Monte gelo
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We show, considering a specific f (R)-gravity model, that the Jordan frame and the Einstein frame could be physically non-equivalent, although they are connected by a conformal transformation which yields a mathematical equivalence. Calculations are performed analytically and this non-equivalence is shown in an unambiguous way. However this statement strictly depends on the considered physical quantities that have to be carefully selected. © 2010 Elsevier B.V. All rights reserved.

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.

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.

Cardone V.F.,National institute for astrophysics | Piedipalumbo E.,University of Naples Federico II | Piedipalumbo E.,Compl University Monte gelo | Scudellaro P.,University of Naples Federico II | Scudellaro P.,Compl University Monte gelo
Monthly Notices of the Royal Astronomical Society | Year: 2016

Strong lensing provides popular techniques to investigate the mass distribution of intermediate redshift galaxies, testing galaxy evolution and formation scenarios. It especially probes the background cosmic expansion, hence constraining cosmological parameters. The measurement of Einstein radii and central velocity dispersions indeed allows to trace the ratio Ds/Dls between the distance Ds from the observer to the source and the distance Dls from the lens to the source. We present an improved method to explicitly include the two-component structure in the galaxy lens modelling, in order to analyse the role played by the redshift and the model dependence on a nuisance parameter, FE, which is usually marginalized in the cosmological applications. We show how to deal with these problems and carry on a Fisher matrix analysis to infer the accuracy on cosmological parameters achieved by this method. © 2015 The Authors.

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