Description
Organiser: Maximilian von Wietersheim-Kramsta; co organisers: Aristeidis Amvrosiadis, Djuna Lize Croon, Leo Fung, Harshnoor Kaur, David Lagattuta, Samuel Lange, Gavin Leroy, Richard Massey, Nency Patel, Kai Wang
From the distortions of the images of stars due to exoplanets to the coherent warping of the relic radiation from the Big Bang, gravitational lensing (GL) is a phenomenon ingrained in the laws of gravity allowing us to probe astrophysics over a wide range of scales. Upcoming surveys, such as Euclid, Rubin LSST, SKA and Roman, will for the first time map weak GL over the whole sky from billions of sources. Simultaneously, instruments such as JWST, ALMA, ELT and HWO will observe strong GL with unprecedented resolution, while LIGO/VIRGO, LISA and IPTA can measure the impact of GL on gravitational waves. Truly, we are on the cusp of probing gravity, the nature of dark matter and the evolution of the Universe over untested regimes with unparalleled precision.
To mark this golden era in the field, we will bring together expert GL modelers, theorists, and observers to showcase and discuss their research. The session will focus on the scientific impact of GL probes: how they will inform novel theories, prepare the next generation of simulations, and improve data analysis techniques, while addressing current tensions. Through contributed talks, we will hear about a wide range of GL subfields with the aim of fostering collaboration and awareness within the field.
I present the COSMOS-Web Lens Survey (COWLS), a groundbreaking sample of over 100 strong lens candidates identified within the $0.54$deg$^2$ COSMOS-Web survey using high-resolution James Webb Space Telescope (JWST} imaging across four wavebands. Through two rounds of visual inspection and lens modeling, more than 100 candidates were classified as โhigh confidenceโ or โlikelyโ by at least...
In this talk I will review the concept of the line-of-sight (LOS) shear, a model for external shear in strong lensing that is theoretically free from degeneracies with lens model parameters. Measurements of the LOS shear will provide new, independent constraints on cosmological parameters such as $\sigma_8$ via a cross-correlation with traditional weak lensing probes. I will present a...
Characterizing the population and internal structure of sub-galactic haloes is critical for constraining the nature of dark matter. These haloes can be detected near galaxies that act as strong gravitational lenses with extended arcs, as they perturb the shapes of the arcs. However, this method is subject to false-positive detections and systematic uncertainties: particularly degeneracies...
Recent strong lensing analyses have suggested that the dark matter subhalo detected in SDSSJ0946+1006 has an extremely high concentration, which is difficult to reconcile with predictions from the standard cold dark matter (CDM) model. However, previous studies did not properly account for the possible contribution of light from a galaxy embedded within the subhalo, if such a galaxy exists....
This work investigates how the lensing signature and detectability of dark matter subhalos in mock HST and Euclid-like strong lensing observations depends on the subhalo's radial density profile, especially with regards to the inner power-law slope, $\beta$. The inner region of a subhalo's density distribution is particularly sensitive to dark matter microphysics, with alternative dark matter...
The James Webb Space Telescope (JWST) has opened a new frontier in strong gravitational lensing by providing the resolution and depth necessary to identify some of the most distant lenses ever discovered. Among these are group-scale lenses, systems of approximately 2โ10 galaxies that bridge the gap between galaxy- and cluster-scale lenses. These systems offer magnifications up to ten times...
A decade ago, it was forecasted that the Euclid space telescope would discover ~150,000 strong gravitational lenses, revolutionising the field. However, it was previously unknown if it would be possible to extract these from the total 1.5 billion galaxies that Euclid will observe. In the recent early data release (Q1), which represents the first 0.45% of the full Euclid survey, we discovered...
Properties of dark matter (DM) substructures deliver important insight about the interaction among the DM constituents. Detection of DM substructures were made possible in the last decade with a parametric method known as โgravitational imagingโ, yielding successful detections of sub-haloes of mass $M_{sub} > 10^8$ $M_\odot$. For substructures smaller than $10^8 M_\odot$, the detection is...
Dark matter halos, central to much of cosmology and astrophysics, are often summarised by their radial density profiles. These are typically assumed to have a fixed functional form (such as NFW) inspired by simulations, with a number of free parameters that can be constrained by fits to observational data. However, the approach of relying on simulations is undesirable, as the dark matter...
I will review the recent significant advances in statistical learning that have led to gravitational lensing analyses using "simulation-based inference" (SBI). These new statistical approaches permit data analyses that would otherwise be impossible. I will review results from the Kilo-Degree Survey and the Dark Energy Surveys, both using SBI for classical 2pt statistics and also beyond 2pt...
Weak gravitational lensing by large-scale structures offers a powerful technique for directly mapping the distribution of matter in the Universe. Following this principle, we recently produce the highest-resolution dark matter maps of the 0.54 square degree COSMOS-Web field to date. These maps are derived from weak lensing cosmic shear measurements using the James Webb Space Telescope (JWST)...
Gravitational microlensing is a unique probe of the stellar content in strong lens galaxies. Flux ratio anomalies from gravitationally lensed supernovae (glSNe), just like lensed quasars, can be used to constrain the stellar mass fractions at the image positions. Type Ia supernovae are of particular interest as knowledge of the intrinsic source brightness helps constrain the amount of...
We present a proof-of-concept study using lensed stars as a pioneer probe of the high-mass stellar initial mass function (IMF) at z~1 galaxies. Residing at cosmological distances, only the most luminous stars can be detected as a transient event even with the extreme magnification under the strong lensing effect from galaxy clusters and the microlensing effect from foreground intra-cluster...
Supermassive black hole binaries (SMBHB) form in galactic nuclei after galaxy mergers. In this presentation, I will demonstrate that inspiraling SMBHBs detectable with LISA may act as a binary gravitational lens leading to a new class of electromagnetic (EM) counterparts. The caustic (i.e. the curve on which the magnification diverges) of the binary lens is more complex than that of a single...
When a gravitational wave signal encounters a massive object, such as a galaxy or galaxy cluster, it undergoes strong gravitational lensing, producing multiple copies of the original signal. These strongly lensed signals share identical waveform morphology in the frequency domain, enabling analysis without complex lens models. However, stellar fields and dark matter substructures within the...
Individual stars located near the caustics of galaxy clusters can undergo extreme magnification when crossing micro-caustics, making them observable even at cosmological distances. Although most massive stars are likely to reside in binary systems rather than as single stars, the influence of binary star systems on magnification events remains severely underexplored. In this report, I will...
Weak gravitational lensing has become an increasingly powerful probe for constraining cosmological parameters and exploring the nature of dark matter and dark energy. Stage-IV cosmological analyses will require rapid computation of summary statistics across wide angular scales and multiple tomographic bins to enable efficient sampling of high-dimensional parameter spaces.
In this talk, I...
Strong gravitational lensing systems with multiple source planes are powerful tools for probing the density profiles and dark matter substructure of galaxies, as well as the equation of state of dark energy. However, galaxy scale double-source-plane lenses are extremely rare. We have discovered four new galaxy-scale DSPL candidates in the Euclid Quick Release 1 data and several more in the...
Next-generation of galaxy surveys will provide vast datasets to improve our knowledge of the universe once we extract the maximum information content. However, the late-time matter distribution is non-Gaussian, limiting the information captured by two-point statistics. One-point statistics can extract a key part of the non-Gaussian information from galaxy clustering, and combining it with weak...
SBI wih Euclid gives us the potential to perform accurate parameter estimation and model comparison in the field-level setting, allowing us to better determine the true nature of dark energy (Spurio Mancini et al. 2024).
SBI, however, hinges upon both accurate forward modelling as well as compression due to the high-dimensional nature of fields. On the forward modelling side, we present...
The fundamental nature of dark matter so far eludes direct detection experiments, but it has left its imprint in the cosmic large-scale structure. Extracting this information requires accurate modelling of structure formation for different dark matter theories (e.g., the axion), careful handling of astrophysical uncertainties and consistent observations in independent cosmological probes. I...
Strong gravitationally lensed supernovae are exquisite laboratories for studying supernova astrophysics, dark matter in high-z galaxies and measuring the Hubble Constant. Their use in cosmology is predicated on measuring time-delays between multiple images and inferring the lens potential. The Vera C. Rubin Observatory is expected to discover tens of such systems, meaning that the constraints...
Strong gravitationally lensed supernovae (glSNe) are a powerful tool for cosmology and astrophysics. By measuring the time delays between the multiple images of a lensed supernova, we can derive the Hubble constantโprovided we have an accurate model of the lensing galaxyโs gravitational potential. The presence of a lensed host galaxy is crucial for accurately modelling this potential. In this...
While gravitational lensing has been a central tool in astrophysics and cosmology for decades, only with the launch of the Hubble and James Webb Space Telescopes (HST and JWST) have strong lenses been effectively used to probe the high-redshift universe. In JWST Cycle 3, the NIRCam multi-band GLIMPSE survey obtained ultra-deep observations of Abell S1063, one of the most powerful known...
Simulation-based inference (SBI) is emerging as a powerful tool for cosmological inference. However, accurate and robust inference requires large numbers of simulations: both to train neural compression techniques that rely on deep learning models, as well as to fit well calibrated models of the posterior. This poses a challenge when working with expensive, high-fidelity simulations, where...
