Author: Samuel Farrens

I have been a postdoctoral researcher at CEA Saclay since October 2015. I am currently working on the DEDALE project and the Euclid mission with Jean-Luc Starck. My background is in optical detection of clusters of galaxies and photometric redshift estimation. I am now branching out into the field of PSF estimation using sparse signal processing techniques.

TOSCA Postdoctoral position on cosmology (CEA Paris-Saclay): optimising the synergy between Euclid and SKA

Posted on by Samuel Farrens

TOSCA Postdoctoral position on cosmology (CEA Paris-Saclay): optimising the synergy between Euclid and SKA

Position: Postdoc 2+1 years, CEA Paris-Saclay DAp
Deadline:  15/12/2023 starting in 2024 (flexible) 
Contacts: V.Pettorino, M. Kilbinger

Details about this position are provided in the following PDF.

UNIONS: The impact of systematic errors on weak-lensing peak counts

UNIONS: The impact of systematic errors on weak-lensing peak counts

Posted on by Samuel Farrens

 

Authors: E. Ayçoberry, V. Ajani, A. Guinot, M. Kilbinger, V. Pettorino, S. Farrens, J.-L. Starck, R. Gavazzi, M. Hudson
Journal: A&A
Year: 2022
DOI:  
Download: ADS | arXiv

Abstract

Context. The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is an ongoing deep photometric multi-band survey of the Northern sky. As part of UNIONS, the Canada-France Imaging Survey (CFIS) provides r-band data which we use to study weak-lensing peak counts for cosmological inference.
Aims. We assess systematic effects for weak-lensing peak counts and their impact on cosmological parameters for the UNIONS survey. In particular, we present results on local calibration, metacalibration shear bias, baryonic feedback, the source galaxy redshift estimate, intrinsic alignment, and the cluster member dilution.

Methods. For each uncertainty and systematic effect, we describe our mitigation scheme and the impact on cosmological parameter constraints. We obtain constraints on cosmological parameters from MCMC using CFIS data and MassiveNuS N-body simulations as a model for peak counts statistics.
Results. Depending on the calibration (local versus global, and the inclusion of the residual multiplicative shear bias), the mean matter density parameter Ωm can shift up to −0.024 (−0.5σ). We also see that including baryonic corrections can shift Ωm by +0.027 (+0.5σ) with respect to the DM-only simulations. Reducing the impact of the intrinsic alignment and cluster member dilution through signal-to-noise cuts can lead to a shift in Ωm of +0.027 (+0.5σ). Finally, with a mean redshift uncertainty of ∆z ̄ = 0.03, we see that the shift of Ωm (+0.001 which corresponds to +0.02σ) is not significant.

Conclusions. This paper investigates for the first time with UNIONS weak-lensing data and peak counts the impact of systematic effects. The value of Ωm is the most impacted and can shift up to ∼ 0.03 which corresponds to 0.5σ depending on the choices for each systematics. We expect constraints to become more reliable with future (larger) data catalogues, for which the current pipeline will provide a starting point. The code used to obtain the results is available in the following Github repository.

ShapePipe: a new shape measurement pipeline and weak-lensing application to UNIONS/CFIS data

ShapePipe: a new shape measurement pipeline and weak-lensing application to UNIONS/CFIS data

Posted on by Samuel Farrens

 

Authors: A. Guinot, M. Kilbinger, S. Farrens, A. Peel, A. Pujol, M. Schmitz, J.-L. Starck, T. Erben, R. Gavazzi, S. Gwyn, M. Hudson,  H. Hiledebrandt, T. Liaudat , et. al
Journal: A&A
Year: 2022
DOI:  
Download: ADS | arXiv

Abstract

UNIONS is an ongoing collaboration that will provide the largest deep photometric survey of the Northern sky in four optical bands to date. As part of this collaboration, CFIS is taking r-band data with an average seeing of 0.65 arcsec, which is complete to magnitude 24.5 and thus ideal for weak-lensing studies. We perform the first weak-lensing analysis of CFIS r-band data over an area spanning 1700 deg2 of the sky. We create a catalogue with measured shapes for 40 million galaxies, corresponding to an effective density of 6.8 galaxies per square arcminute, and demonstrate a low level of systematic biases. This work serves as the basis for further cosmological studies using the full UNIONS survey of 4800 deg2 when completed. Here we present ShapePipe, a newly developed weak-lensing pipeline. This pipeline makes use of state-of-the-art methods such as Ngmix for accurate galaxy shape measurement. Shear calibration is performed with metacalibration. We carry out extensive validation tests on the Point Spread Function (PSF), and on the galaxy shapes. In addition, we create realistic image simulations to validate the estimated shear. We quantify the PSF model accuracy and show that the level of systematics is low as measured by the PSF residuals. Their effect on the shear two-point correlation function is sub-dominant compared to the cosmological contribution on angular scales <100 arcmin. The additive shear bias is below 5x10−4, and the residual multiplicative shear bias is at most 10−3 as measured on image simulations. Using COSEBIs we show that there are no significant B-modes present in second-order shear statistics. We present convergence maps and see clear correlations of the E-mode with known cluster positions. We measure the stacked tangential shear profile around Planck clusters at a significance higher than 4σ.

La matière noire de la toile cosmique révélée par l’effet de lentille gravitationnelle

La matière noire de la toile cosmique révélée par l’effet de lentille gravitationnelle

Posted on by Samuel Farrens

Une nouvelle étape a été franchie dans le domaine des lentilles gravitationnelles faibles (weak lensing) avec la production d’un des plus riches catalogues de galaxies. Ce catalogue contient la morphologie ultra-précise de 100 millions de galaxies lointaines, permettant de mesurer les déformations infimes causées par le lentillage gravitationnel qui agit sur la lumière se propageant à travers la toile cosmique de matière noire présente dans tout l’Univers.

Une gigantesque cartographie du ciel et un jeu considérable de données pour mieux comprendre la matière noire

Une gigantesque cartographie du ciel et un jeu considérable de données pour mieux comprendre la matière noire

Posted on by Samuel Farrens

Au sein de la collaboration internationale UNIONS, des scientifiques de l’Institut de recherche sur les lois fondamentales de l’Univers du CEA ont produit un des plus grands jeux de données sur la matière noire, provenant de l’observation de 100 millions de galaxies déformées par des lentilles gravitationnelles. Des données très précieuses pour de nombreuses missions scientifiques. 

ShapePipe: A modular weak-lensing processing and analysis pipeline

ShapePipe: A modular weak-lensing processing and analysis pipeline

Posted on by Samuel Farrens

 

Authors: S. Farrens, A. Guinot, M. Kilbinger, T. Liaudat , L. Baumont, X. Jimenez, A. Peel , A. Pujol , M. Schmitz, J.-L. Starck, and A. Z. Vitorelli
Journal: A&A
Year: 2022
DOI: 10.1051/0004-6361/202243970
Download: ADS | arXiv

Abstract

We present the first public release of ShapePipe, an open-source and modular weak-lensing measurement, analysis, and validation pipeline written in Python. We describe the design of the software and justify the choices made. We provide a brief description of all the modules currently available and summarise how the pipeline has been applied to real Ultraviolet Near-Infrared Optical Northern Survey data. Finally, we mention plans for future applications and development. The code and accompanying documentation are publicly available on GitHub.

AMICO galaxy clusters in KiDS-DR3: measurement of the halo bias and power spectrum normalization from a stacked weak lensing analysis

AMICO galaxy clusters in KiDS-DR3: measurement of the halo bias and power spectrum normalization from a stacked weak lensing analysis

Posted on by Samuel Farrens

 

Authors: L. Ingoglia, G. Covone, M. Sereno, ..., S. Farrens, et al.
Journal: MNRAS
Year: 2022
DOI: 10.1093/mnras/stac046
Download: ADS | arXiv

Abstract

Galaxy clusters are biased tracers of the underlying matter density field. At very large radii beyond about 10 Mpc/\textit{h}, the shear profile shows evidence of a second-halo term. This is related to the correlated matter distribution around galaxy clusters and proportional to the so-called halo bias. We present an observational analysis of the halo bias-mass relation based on the AMICO galaxy cluster catalog, comprising around 7000 candidates detected in the third release of the KiDS survey. We split the cluster sample into 14 redshift-richness bins and derive the halo bias and the virial mass in each bin by means of a stacked weak lensing analysis. The observed halo bias-mass relation and the theoretical predictions based on the \\Lambda\CDM standard cosmological model show an agreement within \2\sigma\. The mean measurements of bias and mass over the full catalog give \M_{200c} = (4.9 \pm 0.3) \times 10^{13} M_{\odot}/\textit{h}\ and \b_h \sigma_8^2 = 1.2 \pm 0.1\. With the additional prior of a bias-mass relation from numerical simulations, we constrain the normalization of the power spectrum with a fixed matter density \\Omega_m = 0.3\, finding \\sigma_8 = 0.63 \pm 0.10\.