1,721,217 research outputs found
Constraining primordial non-Gaussianity with cosmological weak lensing: shear and flexion
No full textWe examine the cosmological constraining power of future large-scale weak lensing surveys on the model of the ESA planned mission Euclid, with particular reference to primordial non-Gaussianity. Our analysis considers several different estimators of the projected matter power spectrum, based on both shear and flexion. We review the covariance and Fisher matrix for cosmic shear and evaluate those for cosmic flexion and for the cross-correlation between the two. The bounds provided by cosmic shear alone are looser than previously estimated, mainly due to the reduced sky coverage and background number density of sources for the latest Euclid specifications. New constraints for the local bispectrum shape, marginalized over σ8, are at the level of ΔfNL ~ 100, with the precise value depending on the exact multipole range that is considered in the analysis. We consider three additional bispectrum shapes, for which the cosmic shear constraints range from ΔfNL ~ 340 (equilateral shape) up to ΔfNL ~ 500 (orthogonal shape). Also, constraints on the level of non-Gaussianity and on the amplitude of the matter power spectrum σ8 are almost perfectly anti-correlated, except for the orthogonal bispectrum shape for which they are correlated. The competitiveness of cosmic flexion constraints against cosmic shear ones depends by and large on the galaxy intrinsic flexion noise, that is still virtually unconstrained. Adopting the very high value that has been occasionally used in the literature results in the flexion contribution being basically negligible with respect to the shear one, and for realistic configurations the former does not improve significantly the constraining power of the latter. Since the shear shot noise is white, while the flexion one decreases with decreasing scale, by considering high enough multipoles the two contributions have to become comparable. Extending the analysis up to lmax = 20,000 cosmic flexion, while being still subdominant, improves the shear constraints by ~ 10% when added. However on such small scales the highly non-linear clustering of matter, the impact of baryonic physics, and the non-Gaussian part of the covariance matrix make any error estimation uncertain. By considering lower, and possibly more realistic, values of the flexion intrinsic shape noise results in flexion constraining power being a factor of ~ 2 better than that of shear, and the bounds on σ8 and fNL being improved by a factor of ~ 3 upon their combination
Predicting the Clustering Properties of Galaxy Clusters Detectable by the Planck satellite
No full textWe study the clustering properties of the galaxy clusters detectable by the Planck satellite owing to their thermal Sunyaev-Zel'dovich (SZ) effect. We take the past light-cone effect and the redshift evolution of both the underlying dark matter correlation function and the cluster bias factor into account. A theoretical mass-temperature relation allows us to convert the sensitivity limit of a catalogue into a minimum mass for the dark matter haloes hosting the clusters. We confirm that the correlation length is an increasing function of the sensitivity limits defining the survey. Using the expected characteristics of the Planck cluster catalogue, which will be a quite large and unbiased sample, we predict the two-point correlation function and power spectrum for different cosmological models. We show that the wide redshift distribution of the Planck survey will allow us to constrain the cluster clustering properties up to z~ 1. The dependence of our results on the main cosmological parameters (the matter density parameter, the cosmological constant and the normalization of the density power spectrum) is extensively discussed. We find that future Planck clustering data will place only mild constraints on the cosmological parameters, because the results depend on the physical characteristics of the intracluster medium, like the baryon fraction and the mass-temperature relation. Once the cosmological model and the Hubble constant are determined, the clustering data will allow a determination of the baryon fraction with an accuracy of a few per cent
MOKA: a new tool for strong lensing studies
No full textStrong gravitational lensing is a powerful tool that can be used to probe the matter distribution in the cores of massive dark matter haloes. Recent and ongoing analyses of galaxy cluster surveys - such as the Massive Cluster Survey (MACS), the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), the Sloan Digital Sky Survey (SDSS), the Sloan Giant Arcs Survey (SGAS), the Cluster Lensing and Supernova Survey with Hubble (CLASH) and the Local Cluster Substructure Survey (LoCuSS) - have addressed the question of the nature of the dark matter distribution in clusters. Using N-body simulations of cold dark matter haloes, it is consistently found that haloes should be characterized by a concentration-mass relation, which decreases monotonically with halo mass, and that they should be populated by a large amount of substructures, representing the cores of accreted progenitor halos. It is important for our understanding of dark matter that we test these predictions. We present MOKA, a new algorithm for simulating the gravitational lensing signal from cluster-sized haloes. It implements the most recent results from numerical simulations to create realistic cluster-scale lenses with properties independent of numerical resolution. We perform systematic studies of the strong lensing cross-section as a function of halo structures. We find that the strong lensing cross-sections depend most strongly on the concentration and on the inner slope of the density profile of a halo, followed in order of importance by halo triaxiality and the presence of a bright central galaxy
Structure formation in cosmologies with oscillating dark energy
No full textWe study the imprints on the formation and evolution of cosmic structures of a particular class of dynamical dark energy models, characterized by an oscillating equation of state. This investigation complements earlier work on the topic that focused exclusively on the expansion history of the Universe for such models. Oscillating dark energy cosmologies were introduced in an attempt to solve the coincidence problem, since in the course of cosmic history matter and dark energy would have had periodically comparable energy densities. In this class of models the redshift evolution of the equation of state parameter w(z) for dark energy is characterized by two parameters, describing the amplitude and the frequency of the oscillations (the phase is usually set by the boundary condition that w(z) should be close to -1 at recent times). We consider six different oscillating dark energy models, each characterized by a different set of parameter values. For one of these models w(z) is lower than -1 at present and larger than -1 in the past, in agreement with some marginal evidence from recent Type Ia supernova studies. Under the common assumption that dark energy is not clustering on the scales of interest, we study different aspects of cosmic structure formation. In particular, we self-consistently solve the spherical collapse problem based on the Newtonian hydrodynamical approach, and compute the resulting spherical overdensity as a function of cosmic time. We then estimate the behaviour of several cosmological observables, such as the linear growth factor, the integrated Sachs-Wolfe effect, the number counts of massive structures and the matter and cosmic shear power spectra. We show that, independently of the amplitude and the frequency of the dark energy oscillations, none of the aforementioned observables shows an oscillating behaviour as a function of redshift. This is a consequence of the said observables' being integrals over some functions of the expansion rate over cosmic history, thus smoothing any oscillatory features in w(z) below detectability. We also notice that deviations with respect to the expectations for a fiducial Λ cold dark matter cosmology are generically small, and in the majority of the cases distinguishing an oscillating dark energy model would be difficult. Exceptions to this conclusion are provided by the cosmic shear power spectrum, which for some of the models shows a difference at the level of ̃10 per cent over a wide range of angular scales, and the abundance of galaxy clusters, which is modified at the ̃10-20 per cent level at z≳ 0.6 for future wide weak lensing surveys
Effects of cluster galaxies on arc statistics
No full textWe present the results of a set of numerical simulations evaluating the effect of cluster galaxies on arc statistics. We perform a first set of gravitational lensing simulations using three independent projections for each of nine different galaxy clusters obtained from N-body simulations. The simulated clusters consist of dark matter only. We add a population of galaxies to each cluster, mimicking the observed luminosity function and the spatial galaxy distribution, and repeat the lensing simulations including the effects of cluster galaxies, which themselves act as individual lenses. Each galaxy is represented by a spherical Navarro, Frenk & White density profile. We consider the statistical distributions of the properties of the gravitational arcs produced by our clusters with and without galaxies. We find that the cluster galaxies do not introduce perturbations strong enough to significantly change the number of arcs and the distributions of lengths, widths, curvature radii and length-to-width ratios of long arcs. We find some changes to the distribution of short-arc properties in the presence of cluster galaxies. The differences appear in the distribution of curvature radii for arc lengths smaller than 12arcsec, while the distributions of lengths, widths and length-to-width ratios are significantly changed only for arcs shorter than 4arcsec
The impact of cluster mergers on arc statistics
No full textWe study the impact of merger events on the strong lensing properties of galaxy clusters. Previous lensing simulations were not able to resolve dynamical time-scales of cluster lenses, which arise on time-scales that are of the order of a Gyr. In this case study, we first describe qualitatively with an analytic model how some of the lensing properties of clusters are expected to change during merging events. We then analyse a numerically-simulated lens model for the variation in its efficiency for producing both tangential and radial arcs while a massive substructure falls on to the main cluster body. We find that: during the merger, the shape of the critical lines and caustics changes substantially; the lensing cross-sections for long and thin arcs can grow by one order of magnitude and reach their maxima when the extent of the critical curves is largest; the cross-section for radial arcs also grows, but the cluster can efficiently produce these kind of arcs only while the merging substructure crosses the main cluster centre, and while the arc cross-sections pass through their maxima as the merger proceeds, the X-ray emission of the cluster increases by a factor of ~5. Thus, we conclude that accounting for these dynamical processes is very important for arc statistics studies. In particular, they may provide a possible explanation for the arc statistics problem
Halo concentrations and weak-lensing number counts in dark energy cosmologies
No full textWe study the effects of a dark energy component with equation of state p = wrho with constant w greater than or equal to -1 on the formation of Cold Dark Matter (CDM) haloes. We find two main effects: first, haloes form earlier as w increases, and second, the amplitude of the dark-matter power spectrum gets reduced in order to remain compatible with the large scale Cosmic Microwave Background (CMB) anisotropies. These effects counteract. Using recipes derived from numerical simulations, we show that haloes are expected to be up to similar to50% more concentrated in CDM models with quintessence compared to LambdaCDM models, the maximum increase being reached for w similar to -0.6. For larger w, the amplitude of the power spectrum decreases rapidly and makes expected halo concentrations decrease. Halo detections through weak gravitational lensing are highly sensitive to halo concentrations. We show that weak-lensing halo counts with the aperture-mass technique increase by a factor of similar to2 as w is increased from -1 to - 0.6, offering a new method for constraining the nature of dark energy
Observing the clustering properties of galaxy clusters in dynamical-dark energy cosmologies
No full textWe study the clustering properties of galaxy clusters expected to be observed by various forthcoming surveys both in the X-ray and sub-mm regimes by the thermal Sunyaev-Zel'dovich effect. Several different background cosmological models are assumed, including the concordance ΛCDM and various cosmologies with dynamical evolution of the dark energy. Particular attention is paid to models with a significant contribution of dark energy at early times which affects the process of structure formation. Past light cone and selection effects in cluster catalogs are carefully modeled by realistic scaling relations between cluster mass and observables and by properly taking into account the selection functions of the different instruments. The results show that early dark-energy models are expected to produce significantly lower values of effective bias and both spatial and angular correlation amplitudes with respect to the standard ΛCDM model. Among the cluster catalogs studied in this work, it turns out that those based on eRosita, Planck, and South Pole Telescope observations are the most promising for distinguishing between various dark-energy models
Arc statistics with numerical cluster models in of dark energy cosmologies
No full textWe perform a set of ray-tracing simulations, using numerical cluster models, aiming at evaluating how the galaxy cluster efficiency for producing strong lensing events changes in different cosmological models with dark energy. The sample of investigated clusters for which we present our results here is composed by 7 dark matter halos. Each of them was simulated in 8 different cosmological models with constant and time-variable equation of state of dark energy. For all the clusters in the sample, we have measured the lensing cross sections for producing giant arcs, i.e. arcs having a minimum length-to-width ratio. We find that the lensing cross section for giant arcs is sensitive to the equation of state of quintessence. Indeed, the optical depth, which can be translated into a number of arcs by multiplying by the correct density of source galaxy on the sky, spans more than one order of magnitude among different cosmological models
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