[en] We present the current status of cosmological weak lensing studies. Theoretical expectations and observational results are discussed in the framework of standard cosmology and CDM scenarios. We show that present-day surveys already provide important clues and new constraints on cosmological parameters and on the biasing. Finally, the potentials of the next generation cosmic shear surveys are discussed

[en] We study the sensitivity of weak lensing by large scale structures as a probe of the evolution of dark energy. We explore a two-parameters model of dark energy evolution, inspired by tracking quintessence models. To this end, we compute the likelihood of a few fiducial models with varying and nonvarying equation of states. For the different models, we investigate the dark energy parameter degeneracies with the mass power spectrum shape Γ, normalization σ₈, and with the matter mean density Ω_M. We find that degeneracies are such that weak lensing turns out to be a good probe of dark energy evolution, even with limited knowledge on Γ, σ₈, and Ω_M. This result is a strong motivation for performing large scale structure simulations beyond the simple constant dark energy models, in order to calibrate the nonlinear regime accurately. Such calibration could then be used for any large scale structure tests of dark energy evolution. Prospective for the Canada France Hawaii Telescope Legacy Survey and Super-Novae Acceleration Probe are given. These results complement nicely the cosmic microwave background and supernovae constraints

[en] The cross correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and gravitational lensing in wide field has recently been measured. It can be used to probe the distribution of the diffuse gas in large scale structure, as well as inform us about the missing baryons. As for any lensing-based quantity, higher order lensing effects can potentially affect the signal. Here, we extend previous higher order lensing calculations to the case of tSZ-lensing cross correlations. We derive terms analogous to corrections due to the Born approximation, lens-lens coupling, and reduced shear up to order ℓ ∼> 3000

[en] Approximately half of the Universe's baryons are in a form that has been hard to detect directly. However, the missing component can be traced through the cross-correlation of the thermal Sunyaev-Zeldovich (tSZ) effect with weak gravitational lensing. We build a model for this correlation and use it to constrain the extended baryon component, employing data from the Canada France Hawaii Lensing Survey and the Planck satellite. The measured correlation function is consistent with an isothermal β-model for the halo gas pressure profile, and the 1- and 2-halo terms are both detected at the 4σ level. In addition, we measure the hydrostatic mass bias (1−b)=0.79"+"0"."0"7_−_0_._1_0, which is consistent with numerical simulation results and the constraints from X-ray observations. The effective temperature of the gas is found to be in the range (7×10"5–3 ×10"8) K, with approximately 50% of the baryons appearing to lie beyond the virial radius of the halos, consistent with current expectations for the warm-hot intergalactic medium

[en] Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening matter. The distortions are due to fluctuations in the gravitational potential, and are directly related to the distribution of matter and to the geometry and dynamics of the Universe. As a consequence, weak gravitational lensing offers unique possibilities for probing the Dark Matter and Dark Energy in the Universe. In this review, we summarise the theoretical and observational state of the subject, focussing on the statistical aspects of weak lensing, and consider the prospects for weak lensing surveys in the future. Weak gravitational lensing surveys are complementary to both galaxy surveys and cosmic microwave background (CMB) observations as they probe the unbiased non-linear matter power spectrum at modest redshifts. Most of the cosmological parameters are accurately estimated from CMB and large-scale galaxy surveys, so the focus of attention is shifting to understanding the nature of Dark Matter and Dark Energy. On the theoretical side, recent advances in the use of 3D information of the sources from photometric redshifts promise greater statistical power, and these are further enhanced by the use of statistics beyond two-point quantities such as the power spectrum. The use of 3D information also alleviates difficulties arising from physical effects such as the intrinsic alignment of galaxies, which can mimic weak lensing to some extent. On the observational side, in the next few years weak lensing surveys such as CFHTLS, VST-KIDS and Pan-STARRS, and the planned Dark Energy Survey, will provide the first weak lensing surveys covering very large sky areas and depth. In the long run even more ambitious programmes such as DUNE, the Supernova Anisotropy Probe (SNAP) and Large-aperture Synoptic Survey Telescope (LSST) are planned. Weak lensing of diffuse components such as the CMB and 21 cm emission can also provide valuable cosmological information. Finally, we consider the prospects for joint analysis with other probes, such as (1) the CMB to probe background cosmology (2) galaxy surveys to probe large-scale bias and (3) Sunyaev-Zeldovich surveys to study small-scale baryonic physics, and consider the lensing effect on cosmological supernova observations

[en] We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) y-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, ξ_y_κ(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (0θ ∼< 1 arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as σ_8, Ω_m and Ω_b). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass (M_h_a_l_o ∼< 10"1"4 M_⊙) clusters as well as from the region beyond the virial radius. We estimate that approximately 20% of the detected signal comes from low-mass clusters, which corresponds to about 30% of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos (∼> 5 times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models

[en] Relativistic jets from AGN have a wide range of impacts on galaxy groups and clusters and are key for understanding their formation and physical properties. However, this non-gravitational process is not well understood. Galaxy groups with shallow gravitational potentials are ideal laboratories to study and constrain the AGN feedback model. We studied hot gas in ∼66,000 SDSS LRG halos with an average halo mass of 3×10¹³ M_⊙ using the Planck tSZ map. We have detected their average tSZ radial profile at ∼17σ and compared it with the cosmo-OWLS cosmological hydrodynamical simulations with different AGN feedback models. The best agreement has been obtained for the AGN 8.0 model in the simulations. We have also compared our measured tSZ profile with the prediction from the universal pressure profile assuming the self-similar relation and found them consistent if the model accounts for the clustering of neighboring haloes via a two-halo term.

[en] We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey (NGVS) using our detection algorithm RedGOLD. The NGVS covers 104 deg² of the Virgo cluster in the $u^{\ast <!--\; ???\; -->},g,r,i,z$-bandpasses to a depth of g ∼ 25.7 mag (5σ). Part of the survey was not covered or has shallow observations in the r band. We build two cluster catalogs: one using all bandpasses, for the fields with deep r-band observations (∼20 deg²), and the other using four bandpasses ($u^{\ast <!--\; ???\; -->},g,i,z$) for the entire NGVS area. Based on our previous Canada–France–Hawaii Telescope Legacy Survey W1 studies, we estimate that both of our catalogs are ∼100% (∼70%) complete and ∼80% pure, at z ≤ 0.6 (z ≲ 1), for galaxy clusters with masses of M ≳ 10¹⁴ M _⊙. We show that when using four bandpasses, though the photometric redshift accuracy is lower, RedGOLD detects massive galaxy clusters up to z ∼ 1 with completeness and purity similar to the five-band case. This is achieved when taking into account the bias in the richness estimation, which is ∼40% lower at 0.5 ≤ z < 0.6 and ∼20% higher at 0.6 < z < 0.8, with respect to the five-band case. RedGOLD recovers all the X-ray clusters in the area with mass M ₅₀₀ > 1.4 × 10¹⁴ M _⊙ and 0.08 < z < 0.5. Because of our different cluster richness limits and the NGVS depth, our catalogs reach lower masses than the published redMaPPer cluster catalog over the area, and we recover ∼90%–100% of its detections.

[en] We present a new measurement of the mass–concentration relation and the stellar-to-halo mass ratio over the halo-mass range 5 × 10¹² to 2 × 10¹⁴ M _⊙. To achieve this, we use weak lensing measurements from the Canada–France–Hawaii Telescope Stripe 82 Survey (CS82), combined with the central galaxies from the redMaPPer cluster catalog and the LOWZ/CMASS galaxy sample of the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Tenth Data Release. The stacked lensing signals around these samples are modeled as a sum of contributions from the central galaxy, its dark matter halo, and the neighboring halos, as well as a term for possible centering errors. We measure the mass–concentration relation: $c_{200c}(M)=A{\left(\frac{M_{200c}}{M_0}\right)}^B$ with A = 5.24 ± 1.24, B = −0.13 ± 0.10 for 0.2 < z < 0.4, and A = 6.61 ± 0.75, B = −0.15 ± 0.05 for 0.4 < z < 0.6. These amplitudes and slopes are completely consistent with predictions from recent simulations. We also measure the stellar-to-halo mass ratio for our samples, and find results consistent with previous measurements from lensing and other techniques.

[en] We measured stacked weak lensing cluster masses for a sample of 1323 galaxy clusters detected by the RedGOLD algorithm in the Canada–France–Hawaii Telescope Legacy Survey W1 and the Next Generation Virgo Cluster Survey at $0.2<<!--\; <\; -->z<<!--\; <\; -->0.5$, in the optical richness range $10<<!--\; <\; -->\mathrm{\lambda <!--\; ??\; -->}<<!--\; <\; -->70$. This is the most comprehensive lensing study of a $\sim <!--\; ???\; -->100\mathrm{\%<!--\; \%\; -->}$ complete and $\sim <!--\; ???\; -->80\mathrm{\%<!--\; \%\; -->}$ pure optical cluster catalog in this redshift range. We test different mass models, and our final model includes a basic halo model with a Navarro Frenk and White profile, as well as correction terms that take into account cluster miscentering, non-weak shear, the two-halo term, the contribution of the Brightest Cluster Galaxy, and an a posteriori correction for the intrinsic scatter in the mass–richness relation. With this model, we obtain a mass–richness relation of $\mathrm{l}\mathrm{o}\mathrm{g}{M}_{200}/M_{\odot <!--\; ???\; -->}=(14.46\pm <!--\; ??\; -->0.02)+(1.04\pm <!--\; ??\; -->0.09)\mathrm{l}\mathrm{o}\mathrm{g}(\mathrm{\lambda <!--\; ??\; -->}/40)$ (statistical uncertainties). This result is consistent with other published lensing mass–richness relations. We give the coefficients of the scaling relations between the lensing mass and X-ray mass proxies, L _X and T _X, and compare them with previous results. When compared to X-ray masses and mass proxies, our results are in agreement with most previous results and simulations, and consistent with the expected deviations from self-similarity.