Alexandre Réfrégier
A5026330747- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Cosmology and Gravitation Theories
- Adaptive optics and wavefront sensing
- Gamma-ray bursts and supernovae
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Stellar, planetary, and galactic studies
- Dark Matter and Cosmic Phenomena
- Scientific Research and Discoveries
- Astrophysical Phenomena and Observations
- CCD and CMOS Imaging Sensors
- Pulsars and Gravitational Waves Research
- Computational Physics and Python Applications
- Astronomical Observations and Instrumentation
- History and Developments in Astronomy
- Gaussian Processes and Bayesian Inference
- Calibration and Measurement Techniques
- Solar and Space Plasma Dynamics
- Black Holes and Theoretical Physics
- Advanced Data Storage Technologies
- Superconducting and THz Device Technology
- Statistical and numerical algorithms
- Geophysics and Gravity Measurements
- Particle physics theoretical and experimental studies
ETH Zurich
2015-2024
Institute of Particle Physics
2022
Board of the Swiss Federal Institutes of Technology
2012-2018
Astronomy and Space
2018
NGC Aerospace (Canada)
2016
University of Zurich
2016
University of Manchester
2016
Institute of Astronomy
2000-2012
CEA Paris-Saclay
2003-2010
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2003-2010
We use 26×106 galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg2 of sky to produce most significant measurement cosmic shear in a galaxy survey date. constrain cosmological parameters both flat ΛCDM and wCDM models, while also varying neutrino mass density. These results are shown be robust using two independent catalogs, photo-z calibration methods, analysis pipelines blind analysis. find 3.5% fractional uncertainty on σ8(Ωm/0.3)0.5=0.782+0.027−0.027 at 68%...
We report a detection of the coherent distortion faint galaxies arising from gravitational lensing by foreground structures. This ``cosmic shear'' is potentially most direct measure mass power spectrum, as it unaffected poorly-justified assumptions made concerning biasing distribution. Our based on an initial imaging study 14 separated 8' x 16' fields observed in good, homogeneous conditions with prime focus EEV CCD camera 4.2m William Herschel Telescope. detect rms shear 1.6% cells,...
The Cosmic Evolution Survey (COSMOS) was initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope (HST) for high resolution imaging. Here we review characteristics of HST imaging Advanced Camera Surveys (ACS) and parallel observations NICMOS WFPC2. A square field (1.8$\sq$\deg) has been imaged single-orbit ACS I-F814W exposures 50% completeness sources 0.5\arcsec diameter at I$_{AB} $ = 26.0 mag. is a key part COSMOS survey, providing very...
The Shear TEsting Programme, STEP, is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for next generation wide-field surveys. In this first STEP paper we present results blind analysis simulated ground-based observations relatively simple galaxy morphologies. most successful methods are shown achieve percent level accuracy. From cosmic shear pipelines that have been used constrain cosmology, find measured an within statistical...
With a primary goal of conducting precision weak lensing measurements from space, the COSMOS survey has imaged largest contiguous area observed by Hubble Space Telescope (HST) to date using Advanced Camera for Surveys (ACS). This is first paper in series where we describe our strategy addressing various technical challenges production data. The ACS catalog constructed 575 ACS/WFC tiles (1.64 deg^2) and contains total 1.2x10^6 objects limiting magnitude F814W=26.5. made publicly available....
This work, together with its companion paper, Secco and Samuroff et al. (2021), presents the Dark Energy Survey Year 3 cosmic shear measurements cosmological constraints based on an analysis of over 100 million source galaxies. With data spanning 4143 deg$^2$ sky, divided into four redshift bins, we produce highest significance measurement to date, a signal-to-noise 40. We conduct blind in context $\Lambda$CDM model find 3% constraint clustering amplitude, $S_8\equiv \sigma_8 (\Omega_{\rm...
We present the first constraints on cosmology from Dark Energy Survey (DES), using weak lensing measurements preliminary Science Verification (SV) data. use 139 square degrees of SV data, which is less than 3% full DES survey area. Using cosmic shear 2-point over three redshift bins we find ${\ensuremath{\sigma}}_{8}({\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}/0.3{)}^{0.5}=0.81\ifmmode\pm\else\textpm\fi{}0.06$ (68% confidence), after marginalizing 7 systematics parameters and 3 other...
We present weak lensing shear catalogues for 139 square degrees of data taken during the Science Verification (SV) time new Dark Energy Camera (DECam) being used Survey (DES). describe our object selection, point spread function estimation and measurement procedures using two independent pipelines, im3shape ngmix, which produce 2.12 million 3.44 galaxies, respectively. detail a set null tests measurements find that they pass requirements systematic errors at level necessary science...
▪ Abstract Weak gravitational lensing provides a unique method to map directly the distribution of dark matter in universe and measure cosmological parameters. This cosmic-shear technique is based on measurement weak distortions that induces shape background galaxies as photons travel through large-scale structures. now widely used mass galaxy clusters has recently been detected random regions sky. In this review, we present theory observational status cosmic shear. We describe principles...
The Shear TEsting Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak lensing measurement, in preparation for next generation wide-field surveys. We review sixteen current emerging shear measurement methods common language, assess their performance by running them (blindly) on simulated images that contain known signal. determine features algorithms most successfully recover input parameters. achieve previously unattained discriminatory precision our...
Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with the halo mass function and understanding physical processes that govern heating cooling intracluster medium. In this paper, we use a sample 206 selected galaxy groups to investigate relation between luminosity (Lx) (M00) where M200 is via stacked weak gravitational lensing. This work draws upon broad array multi-wavelength COSMOS observations including 1.64 square degrees contiguous imaging...
Weak gravitational lensing is now established as a powerful method to measure mass fluctuations in the universe. It relies on measurement of small coherent distortions images background galaxies. Even low-level correlations intrinsic shapes galaxies could however produce significant spurious signal. These are also interesting their own right, since detection would constrain models galaxy formation. Using haloes found N-body simulations, we compute correlation functions ellipticity spiral...
We present a three-dimensional cosmic shear analysis of the Hubble Space Telescope COSMOS survey, largest ever optical imaging program performed in space. have measured shapes galaxies for telltale distortions caused by weak gravitational lensing and traced growth that signal as function redshift. Using both 2D 3D analyses, we measure cosmological parameters Ωm, density matter universe, σ8, normalization power spectrum. The introduction redshift information tightens constraints factor 3 also...
We present a new method for the analysis of images, fundamental task in observational astronomy. It is based on linear decomposition each object image into series localized basis functions different shapes, which we call 'shapelets'. A particularly useful set complete and orthonormal shapelets that consisting weighted Hermite polynomials, correspond to perturbations around circular Gaussian. They are also eigenstates two dimensional quantum harmonic oscillator, thus allow us use powerful...
We present the results of GREAT08 Challenge, a blind analysis challenge to infer weak gravitational lensing shear distortions from images. The primary goal was stimulate new ideas by presenting problem researchers outside measurement community. Six Team methods were presented at launch Challenge and five additional groups submitted during 6 month competition. Participants analyzed 30 million simulated galaxies with range in signal noise ratio, point-spread function ellipticity, galaxy size,...
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area some 5deg2 out to redshift z=1.05. The clusters, which represent about half X-ray identified in region, follow well defined selection criteria and are all spectroscopically confirmed. For we provide luminosities temperatures as masses. cluster distribution peaks around z=0.3 T =1.5 keV, objects being groups with temperature below 2 keV. Our L-T(z) relation points toward self-similar evolution, but does not exclude...
We present photometric redshift estimates for galaxies used in the weak lensing analysis of Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based methods -- ANNZ2, BPZ calibrated against BCC-Ufig simulations, SkyNet, and TPZ are analysed. For training, calibration, testing these methods, we construct a catalogue spectroscopically confirmed matched DES SV The performance is evaluated spectroscopic catalogue, focusing on metrics relevant analyses, with...
In this Letter, we study the implications of string Swampland criteria for dark energy in view ongoing and future cosmological observations. If theory should be ultimate quantum gravity theory, there is evidence that exact de Sitter solutions with a positive constant cannot describe fate late-time universe. Even though models given by scalar field $\pi$ evolving time are not direct tension they have to satisfy $|\Delta\pi|<d\sim\mathcal{O}(1)$ $|V'|/V>c\sim\mathcal{O}(1)$, where $V$...
Shear peak statistics has gained a lot of attention recently as practical alternative to the two point for constraining cosmological parameters. We perform shear analysis Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from 139 deg$^2$ field. measure abundance peaks identified in aperture mass maps, function their signal-to-noise ratio, range $0<\mathcal S / \mathcal N<4$. To predict counts parameters we use suite $N$-body simulations...
The energy density of the Universe is dominated by dark and matter, two mysterious components which pose some most important questions in fundamental science today. Euclid a high-precision survey mission designed to answer these mapping geometry Universe. Euclid's Visible-NIR imaging spectroscopy entire extragalactic sky will further produce extensive legacy for various fields astronomy. Over 2008-2009 period, has been object an ESA Assessment Phase study Imaging instrument was under...
Convolutional neural networks (CNNs) have recently been demonstrated on synthetic data to improve upon the precision of cosmological inference. In particular, they potential yield more precise constraints from weak lensing mass maps than two-point functions. We present results with a CNN KiDS-450 tomographic dataset, constraining total matter density ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}$, fluctuation amplitude ${\ensuremath{\sigma}}_{8}$, and intrinsic alignment ${A}_{\mathrm{IA}}$....
Weak lensing experiments are a powerful probe into cosmology through their measurement of the mass distribution universe. A challenge for this technique is to control systematic errors that occur when measuring shapes distant galaxies. In paper, we investigate noise bias, error arises from second-order terms in shape process. We first derive analytical expressions bias general maximum-likelihood estimators presence additive noise. then find simplified toy model which galaxies modelled and...
Dark matter in the universe evolves through gravity to form a complex network of halos, filaments, sheets and voids, that is known as cosmic web. Computational models underlying physical processes, such classical N-body simulations, are extremely resource intensive, they track action an expanding using billions particles tracers distribution. Therefore, upcoming cosmology experiments will face computational bottleneck may limit exploitation their full scientific potential. To address this...