The Next Generation Virgo Cluster Survey. XX. RedGOLD Background Galaxy Cluster Detections

We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey (NGVS) using our detection algorithm RedGOLD. The NGVS covers 104 deg^2 of the Virgo cluster in the u*, 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 deg^2), and the other using four bandpasses (u*, 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 ≳ 10^(14) 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 1.4 × 10^(14) 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

Relation d’échelle d'amas de galaxies à partir d'observations de lentilles gravitationnelles

Galaxy clusters are essential cosmological and astrophysical tools, since they represent the largest and most massive gravitationally bound structures in the Universe. Through the study of their mass function, of their correlation function, and of the scaling relations between their mass and different observables, we can probe the predictions of cosmological models and structure formation scenarios. They are also interesting laboratories that allow us to study galaxy formation and evolution, and their interactions with the intra-cluster medium, in dense environments. For all of these goals, an accurate estimate of cluster masses is of fundamental importance. I studied the accuracy of the optical richness obtained by the RedGOLD cluster detection algorithm (Licitra et al. 2016) as a mass proxy, using weak lensing and X-ray mass measurements. I measured stacked weak lensing cluster masses for a sample of 1323 galaxy clusters in the CFHTLS W1 and in the NGVS at 0.2<z<0.5, in the optical richness range 10-70. I tested different weak lensing mass models that account for miscentering, non-weak shear, the two-halo term, the contribution of the Brightest Cluster Galaxy, and the intrinsic scatter in the mass-richness relation. I found that the miscentering correction is necessary to avoid a bias in the measured halo masses, while the inclusion of the BCG mass does not affect the results. I calculated the coefficients of the mass-richness relation, and of the scaling relations between the lensing mass and X-ray mass proxies. My results are consistent with simulations and previous works in the literature.Les amas de galaxies sont des outils cosmologiques et astrophysiques essentiels, car ce sont les objets les plus grands et les plus massifs gravitationnellement liées dans l'Univers. L'étude de leur fonction de masse, de leur fonction de corrélation et des relations d'échelle entre leur masse et différentes observables nous permettent de tester les prévisions des modèles cosmologique et les scenarii de formation des structures. Ils sont aussi d'intéressants laboratoires pour l'étude de la formation et de l'évolution des galaxies, et de leur interactions avec le milieu qui les entourent, dans d’environnements denses. Pour y parvenir, estimer précisément leur masse revêt une importance fondamentale. J’ai étudié la précision de la richesse optique calculée par l’algorithme de détection d’amas RedGOLD (Licitra et al. 2016) en tant que mass proxy, en utilisant des mesures de lentilles gravitationnelles (weak lensing) et des observations en rayon X. J’ai mesuré les masses cumulées d’un échantillon de 1323 amas de galaxies dans le CFHTLS et NGVS à 0.2<z<0.5, dans l’intervalle de richesse 10-70. J'ai testé différents modèles prenant en compte les erreurs sur la position du centre de l'amas, les effets de lentille non faible (non-weak shear), le "two-halo term", la contribution de la galaxie centrale brillante et la dispersion intrinsèque de la relation masse-richesse. J'ai montré que la correction de la position du centre est nécessaire pour éviter un biais dans la mesure de la masse, alors que l'ajout de la galaxie centrale n'affecte pas les résultats. J'ai calculer les coefficients de la relation masse-richesse et ceux de la relation d'échelle entre masses issues du weak lensing et celle estimées à partir d'observations dans les rayons X. Mes résultats sont en accord avec les simulations et les précédents travaux publiés

Going deep with Minkowski functionals of convergence maps

International audienceAims. Stage IV lensing surveys promise to make an unprecedented amount of excellent data available. This will represent a huge leap in terms of quantity and quality and will open the way for the use of novel tools that surpass the standard second-order statistics for probing the high-order properties of the convergence field. Motivated by these considerations, some of us have started a long-term project aiming at using Minkowski functionals (MFs) as complementary and supplementary probes to increase the lensing figure of merit (FoM).Methods. As a second step on this path, we discuss the use of MFs for a survey consisting of a wide total area Atot that is imaged at a limiting magnitude magW and contains a subset of area Adeep, where observations are pushed to a deeper limiting magnitude magD. We present an updated procedure to match the theoretically predicted MFs to the measured MFs, and take the effect of map reconstruction from noisy shear data into account. We validate this renewed method against simulated datasets with different source redshift distributions and total number density, setting these quantities in accordance with the depth of the survey. We can then rely on a Fisher matrix analysis to forecast the improvement in the FoM that is due to the joint use of shear tomography and MFs under different assumptions on (Atot,  Adeep, and magD), and the prior on the MFs nuisance parameters.Results. We find that MFs can provide valuable help in increasing the FoM of the lensing survey when the nuisance parameters are known with non-negligible precision. The possibility of compensating for the loss of FoM through a cut in the multipole range that is probed by shear tomography is even more interesting. This makes the results more robust against uncertainties in the modeling of nonlinearities. This makes MFs a promising tool for increasing the FoM and also protects the constraints on the cosmological parameters mainly from theoretical systematic effects.Key words: gravitational lensing: weak / cosmology: theory / methods: statistica

Higher-order statistics of shear field via a machine learning approach

International audienceContext. The unprecedented amount and the excellent quality of lensing data expected from upcoming ground and space-based surveys present a great opportunity for shedding light on questions that remain unanswered with regard to our universe and the validity of the standard ΛCDM cosmological model. The development of new techniques that are capable of exploiting the vast quantity of data provided by future observations, in the most effective way possible, is of great importance.Aims. This is the reason we chose to investigate the development of a new method for treating weak-lensing higher-order statistics, which are known to break the degeneracy among cosmological parameters thanks to their capacity to probe non-Gaussian properties of the shear field. In particular, the proposed method applies directly to the observed quantity, namely, the noisy galaxy ellipticity.Methods. We produced simulated lensing maps with different sets of cosmological parameters and used them to measure higher-order moments, Minkowski functionals, Betti numbers, and other statistics related to graph theory. This allowed us to construct datasets with a range of sizes, levels of precision, and smoothing. We then applied several machine learning algorithms to determine which method best predicts the actual cosmological parameters associated with each simulation.Results. The most optimal model turned out to be a simple multidimensional linear regression. We use this model to compare the results coming from the different datasets and find that we can measure, with a good level of accuracy, the majority of the parameters considered in this study. We also investigated the relation between each higher-order estimator and the different cosmological parameters for several signal-to-noise thresholds and redshifts bins.Conclusions. Given the promising results we obtained, we consider this approach a valuable resource that is worthy of further development.Key words: gravitational lensing: weak / cosmology: theory / methods: statistica

Next Generation Virgo Cluster Survey. XXI. The weak lensing masses of the CFHTLS and NGVS RedGOLD galaxy clusters and calibration of the optical richness

International audienceWe 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 $0.2\lt z\lt 0.5$, in the optical richness range $10\lt \lambda \lt 70$. This is the most comprehensive lensing study of a $\sim 100 \%$ complete and $\sim 80 \%$ 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 $\mathrm{log}{M}_{200}/{M}_{\odot }\,=(14.46\pm 0.02)+(1.04\pm 0.09)\mathrm{log}(\lambda /40)$ (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