196,327 research outputs found
Gravitational lensing of the CMB by galaxy clusters
No full textWe adapt a non-linear filter proposed by Hu (2001) for detecting
lensing of the CMB by large-scale structures to recover
surface-density profiles of galaxy clusters from their localised,
weak gravitational lensing effect on CMB fields. Shifting the
band-pass of the filter to smaller scales, and normalising it such
as to reproduce the convergence rather than the deflection angle, we
find that the mean density profile of a sample of 100 clusters can
be recovered to better than 10% from well within the scale radius
to almost the virial radius. The kinetic Sunyaev-Zel'dovich effect
is shown to be a negligible source of error. We test the filter
applying it to data simulated using the characteristics of the
Atacama Cosmology Telescope (ACT), showing that it will be
possible to recover mean cluster profiles outside a radius of
corresponding to ACT's angular resolution
Combining weak and strong lensing in cluster potential reconstruction
No full textWe propose a method for recovering the two-dimensional
gravitational potential of galaxy clusters which combines data from
weak and strong gravitational lensing. A first estimate of the
potential from weak lensing is improved at the approximate locations
of critical curves. The method can be fully linearised and does not
rely on the existence and identification of multiple images. We use
simulations to show that it recovers the surface-mass density
profiles and distributions very accurately,even if critical curves
are only partially known and if their location is realistically
uncertain. We further describe how arcs at different redshifts can
be combined, and how deviations from weak lensing can be included
Effects of the halo concentration distribution on strong-lensing optical depth and X-ray emission
No full textWe use simulated merger trees of galaxy-cluster halos to study the
effect of the halo concentration distribution on strong lensing and X-ray
emission. Its log-normal shape typically found in simulations favors
outliers with high concentration. Since, at fixed mass, more concentrated
halos tend to be more efficient lenses, the scatter in the concentration
increases the strong-lensing optical depth by \la. Within cluster
samples, mass and concentration have counteracting effects on strong lensing
and X-ray emission because the concentration decreases for increasing
mass. Selecting clusters by concentration thus has no effect on the lensing
cross section. The most efficiently lensing and hottest clusters are
typically the least concentrated in samples with a broad mass
range. Among cluster samples with a narrow mass range, however, the most
strongly lensing and X-ray brightest clusters are typically to
more concentrated
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
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
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
Cosmic reionization in dynamic quintessence cosmology
No full textIn this paper, we investigate the effects that a dynamic dark energy component dominant in the universe at late epochs has on reionization. We follow the evolution of H ii regions with the analytic approach of Furlanetto & Oh in two different universes for which we assume the Peebles & Ratra and Brax & Martin quintessence models and we compare our results to the Λ cold dark matter (ΛCDM) scenario. We show that, for a fixed ionization efficiency, at the same cosmological epoch the morphology of bubbles is dominated by high-mass objects and the characteristic size of the ionized regions is slightly smaller than in the ΛCDM model, especially at the latest stages of reionization, due to the higher recombination efficiency. As a consequence, the bubbles' 'epoch of overlap' happens earlier than in ΛCDM. Finally, we show how the different evolution of the H ii regions affects the transmission of the high-z quasi-stellar object spectra, reducing the Lyman flux absorption at small optical depths. © 2008 RAS
Strong-lensing statistics and the power spectrum normalisation
No full textWe use semi-analytic modelling of the galaxy-cluster population and its strong lensing efficiency to explore how the expected abundance of large gravitational arcs on the sky depends on . Our models take all effects into account that have been shown to affect strong cluster lensing substantially, in particular cluster asymmetry, substructure, merging, and variations in the central density concentrations. We show that the optical depth for long and thin arcs increases by approximately one order of magnitude when increases from 0.7 to 0.9, owing to a constructive combination of several effects. Models with high are also several orders of magnitude more efficient in producing arcs at intermediate and high redshifts. Finally, we use realistic source number counts to quantitatively predict the total number of arcs brighter than several magnitude limits in the R and I bands. We confirm that, while ~ 0.9 may come close to the known abundance of arcs, even ~ 0.8 falls short by almost an order of magnitude in reproducing known counts. We conclude that, should ~ 0.8 be confirmed, we would fail to understand the strong-lensing efficiency of the galaxy cluster population, and in particular the abundance of arcs in high-redshift clusters. We argue that early-dark energy or non-Gaussian density fluctuations may indicate one way out of this problem
Arc statistics in cosmological models with dark energy
No full textWe investigate how the probability of the formation of giant arcs in galaxy clusters is expected to change in cosmological models dominated by dark energy with an equation of state p = omegarhoc(2) compared to cosmological-constant or open models. To do so, we use a simple analytic model for arc cross sections based on the Navarro-Frenk-White density profile which we demonstrate reproduces essential features of numerically determined arc cross sections. Since analytic lens models are known to be inadequate for accurate absolute quantifications of arc probabilities, we use them only for studying changes relative to cosmological-constant models. Our main results are (1) the order of magnitude difference between the arc probabilities in low density, spatially flat and open CDM models found numerically is reproduced by our analytic model, and (2) dark-energy cosmologies with omega > -1 increase the arc optical depth by at most a factor of two and are thus unlikely to reconcile arc statistics with spatially flat cosmological models with low matter density
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
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