Publications de Georgios Vernardos

Euclid: The Early Release Observations Lens Search Experiment

Georges Meylan, Frédéric Courbin, Georgios Vernardos, Lucie Anemone Scharré

We investigated the ability of the Euclid telescope to detect galaxy-scale gravitational lenses. To do so, we performed a systematic visual inspection of the 0.7 deg2 Euclid Early Release Observations data towards the Perseus cluster using both the high-re ...

2025

Strong Gravitational Lensing and Microlensing of Supernovae

Georgios Vernardos

Strong gravitational lensing and microlensing of supernovae (SNe) are emerging as a new probe of cosmology and astrophysics in recent years. We provide an overview of this nascent research field, starting with a summary of the first discoveries of strongly ...

2024

Microlensing of Strongly Lensed Quasars

Martin Raoul Robert Millon, Austin Chandler Peel, Georgios Vernardos

Strong gravitational lensing of quasars has the potential to unlock the poorly understood physics of these fascinating objects, as well as serve as a probe of the lensing mass distribution and of cosmological parameters. In particular, gravitational microl ...

Springer2024

Euclid preparation XXXIII. Characterization of convolutional neural networks for the identification of galaxy-galaxy strong-lensing events

Georges Meylan, Frédéric Courbin, Benjamin Yvan Alexandre Clement, Georgios Vernardos

Forthcoming imaging surveys will increase the number of known galaxy-scale strong lenses by several orders of magnitude. For this to happen, images of billions of galaxies will have to be inspected to identify potential candidates. In this context, deep-le ...

Edp Sciences S A2024

Resolving the vicinity of supermassive black holes with gravitational microlensing

Georgios Vernardos

Upcoming wide-field surveys will discover thousands of new strongly lensed quasars which will be monitored with unprecedented cadence by the Legacy Survey of Space and Time (LSST). Many of these quasars will undergo caustic-crossing events over the 10-yr L ...

Oxford Univ Press2024

Accelerating galaxy dynamical modeling using a neural network for joint lensing and kinematic analyses

Aymeric Alexandre Galan, Georgios Vernardos

Strong gravitational lensing is a powerful tool to provide constraints on galaxy mass distributions and cosmological parameters, such as the Hubble constant, H0. Nevertheless, inference of such parameters from images of lensing systems is not trivial as pa ...

Edp Sciences S A2023

Modeling lens potentials with continuous neural fields in galaxy-scale strong lenses

Frédéric Courbin, Georgios Vernardos

Strong gravitational lensing is a unique observational tool for studying the dark and luminous mass distribution both within and between galaxies. Given the presence of substructures, current strong lensing observations demand more complex mass models than ...

EDP SCIENCES S A2023

Constraining quasar structure using high-frequency microlensing variations and continuum reverberation

Frédéric Courbin, Vivien François Bonvin, Martin Raoul Robert Millon, Eric Gérard Guy Paic, Hung-Hsu Chan, Georgios Vernardos

Gravitational microlensing is a powerful tool for probing the inner structure of strongly lensed quasars and for constraining parameters of the stellar mass function of lens galaxies. This is achieved by analysing microlensing light curves between the mult ...

EDP SCIENCES S A2022

Simulating time-varying strong lenses

Georgios Vernardos

We present a self-consistent and versatile forward modelling software package that can produce time series and pixel-level simulations of time-varying strongly lensed systems. The time dimension, which needs to take into account different physical mechanis ...

OXFORD UNIV PRESS2022

Discovery of strongly lensed quasars in the Ultraviolet Near Infrared Optical Northern Survey (UNIONS)

Elodie Marie Charlène Savary, Martin Raoul Robert Millon, Eric Gérard Guy Paic, Hung-Hsu Chan, Karina Alexandra Rojas Olate, Benjamin Yvan Alexandre Clement, Cameron Alexander Campbell Lemon, Georgios Vernardos

We report the discovery of five new doubly imaged lensed quasars from the first 2500 square degrees of the ongoing Canada-France Imaging Survey (CFIS), which is a component of the Ultraviolet Near Infrared Optical Northern Survey. The systems are preselect ...

EDP SCIENCES S A2022

Time-delay estimation in unresolved lensed quasars

Georgios Vernardos

Time-delay cosmography can be used to infer the Hubble parameter H-0 by measuring the relative time delays between multiple images of gravitationally lensed quasars. A few of such systems have already been used to measure H-0: Their time delays were determ ...

OXFORD UNIV PRESS2022

The very knotty lenser: Exploring the role of regularization in source and potential reconstructions using Gaussian process regression

Georgios Vernardos

Reconstructing lens potentials and lensed sources can easily become an underconstrained problem, even when the degrees of freedom are low, due to degeneracies, particularly when potential perturbations superimposed on a smooth lens are included. Regulariza ...

OXFORD UNIV PRESS2022

SEAGLE III: Towards resolving the mismatch in the dark-matter fraction in early-type galaxies between simulations and observations

Matthieu Schaller, Georgios Vernardos

The central dark-matter fraction of galaxies is sensitive to feedback processes during galaxy formation. Strong gravitational lensing has been effective in the precise measurement of the dark-matter fraction inside massive early-type galaxies. Here, we com ...

OXFORD UNIV PRESS2022

Using wavelets to capture deviations from smoothness in galaxy-scale strong lenses

Frédéric Courbin, Aymeric Alexandre Galan, Austin Chandler Peel, Georgios Vernardos

Modeling the mass distribution of galaxy-scale strong gravitational lenses is a task of increasing difficulty. The high-resolution and depth of imaging data now available render simple analytical forms ineffective at capturing lens structures spanning a la ...

EDP SCIENCES S A2022

Search of strong lens systems in the Dark Energy Survey using convolutional neural networks

Frédéric Courbin, Elodie Marie Charlène Savary, Aymeric Alexandre Galan, Hung-Hsu Chan, Karina Alexandra Rojas Olate, Benjamin Yvan Alexandre Clement, Cameron Alexander Campbell Lemon, Georgios Vernardos

We present our search for strong lens, galaxy-scale systems in the first data release of the Dark Energy Survey (DES), based on a color-selected parent sample of 18 745 029 luminous red galaxies (LRGs). We used a convolutional neural network (CNN) to grade ...

EDP SCIENCES S A2022

TDCOSMO VII. Boxyness/discyness in lensing galaxies: Detectability and impact on H-0

Aymeric Alexandre Galan, Georgios Vernardos

In the context of gravitational lensing, the density profile of lensing galaxies is often considered to be perfectly elliptical. Potential angular structures are generally ignored, except to explain flux ratios of point-like sources (i.e. flux ratio anomal ...

EDP SCIENCES S A2022

Strong lensing in UNIONS: Toward a pipeline from discovery to modeling

Frédéric Courbin, Elodie Marie Charlène Savary, Hung-Hsu Chan, Karina Alexandra Rojas Olate, Benjamin Yvan Alexandre Clement, Cameron Alexander Campbell Lemon, Georgios Vernardos

We present a search for galaxy-scale strong gravitational lenses in the initial 2500 square degrees of the Canada-France Imaging Survey (CFIS). We designed a convolutional neural network (CNN) committee that we applied to a selection of 2 344 002 r-band im ...

EDP SCIENCES S A2022

High-quality Strong Lens Candidates in the Final Kilo-Degree Survey Footprint

Georgios Vernardos

We present 97 new high-quality strong lensing candidates found in the final similar to 350 deg(2) that complete the full similar to 1350 deg(2) area of the Kilo-Degree Survey (KiDS). Together with our previous findings, the final list of high-quality candi ...

IOP Publishing Ltd2021