Showing 1–50 of 73 results for author: Collett, T E

Disentangling the dark and stellar mass through precise lens modelling of the JWST observation of lensed quasar WFI2033--4723

Authors: Tian Li, Thomas E. Collett, Coleman M. Krawczyk, Wolfgang J. R. Enzi, Aymeric Galan

Abstract: We use high-resolution JWST/NIRCam imaging and measured time delays to model the quadruply imaged quasar WFI2033--4723 with a composite stellar plus dark-matter mass model. We first construct an elliptical power-law baseline model and recover Fermat-potential differences (fpd) consistent with previous HST-based and JWST-based analyses, providing a reference scale for composite modelling. We then r… ▽ More We use high-resolution JWST/NIRCam imaging and measured time delays to model the quadruply imaged quasar WFI2033--4723 with a composite stellar plus dark-matter mass model. We first construct an elliptical power-law baseline model and recover Fermat-potential differences (fpd) consistent with previous HST-based and JWST-based analyses, providing a reference scale for composite modelling. We then replace the total mass profile with a physically motivated decomposition in which the stellar mass follows a multi-Gaussian expansion of the lens light, with a free radial mass-to-light gradient, and the dark matter is described by a generalized Navarro--Frenk--White (gNFW) halo. Using two external cosmological priors, Planck+DESI and Pantheon+SH0ES, the measured time delays constrain the mass-sheet-transformation freedom that would otherwise damage the stellar--dark-matter decomposition. In both cosmological cases, the stellar normalization lies between the expectations for Chabrier and Salpeter initial mass functions, while the radial mass-to-light gradient is not strongly required by the data (mildly positive). The dark matter halo has an inner slope $γ_{\rm in}\simeq1.3$, steeper than a standard NFW cusp, and the main astrophysical conclusions are insensitive to the adopted cosmological prior. This work shows that composite time-delay lens modelling can effectively separate baryons from dark matter. As a qualitative check, we reverse the logic and use our composite lens model without kinematic information to infer the cosmology instead. However, the strong degeneracy between $H_0$ and the halo scale radius $R_s$ prevents a robust standalone constraint. △ Less

Submitted 9 July, 2026; originally announced July 2026.

Gaussian processes on ray-guided transformed uniform grids for fast, flexible, and auto-differentiable adaptive source reconstruction in lens modelling

Authors: Wolfgang J. R. Enzi, Coleman M. Krawczyk, Tian Li, Thomas E. Collett

Abstract: Strong gravitational lensing constrains cosmology and dark matter, but robust inference requires accurate source reconstruction. The achievable source resolution is highly position-dependent. Adaptive meshes can place resolution where needed, but typically rely on discontinuous operations, such as Delaunay tessellations or Voronoi binning, which can restrict regularization choices and break differ… ▽ More Strong gravitational lensing constrains cosmology and dark matter, but robust inference requires accurate source reconstruction. The achievable source resolution is highly position-dependent. Adaptive meshes can place resolution where needed, but typically rely on discontinuous operations, such as Delaunay tessellations or Voronoi binning, which can restrict regularization choices and break differentiability. In this paper, we present a novel approach for modelling the source on a ray-guided transformed uniform grid (RTU grid), that is adaptive to the lens mass model, auto-differentiable and flexible with respect to the regularization by allowing for an arbitrary choice of power spectrum. We achieve this by defining the source as a Gaussian process on a uniform grid, which is then transformed based on the cumulative distributions of rays traced back to the source plane. This approach ensures that source pixels contain a more uniform number of rays. The approach is fast by leveraging the fast Fourier transform to describe the Gaussian process in Fourier space. We apply this new approach to mock data and show that it achieves comparable fit quality with fewer source pixels, typically corresponding to about a factor of two fewer pixels per dimension, and increases Evidence Lower Bounds (ELBOs) for the same number of pixels. Using the RTU grid only mildly affects the difference in ELBO for models with and without substructures within lens galaxies. A fast, flexible, and auto-differentiable source reconstruction can greatly benefit the analysis of large samples of lens systems, e.g. those found within the Euclid survey △ Less

Submitted 29 June, 2026; originally announced June 2026.

Comments: Submitted to MNRAS, 13 pages, 9 figures, 4 tables

Euclid Quick Data Release (Q1). AstroVink: A vision transformer approach to find strong gravitational lens systems

Authors: Euclid Collaboration, S. H. Vincken, K. Rojas, M. Melchior, N. E. P. Lines, T. E. Collett, A. Verma, P. Holloway, G. Despali, S. Schuldt, R. B. Metcalf, R. Gavazzi, F. Courbin, J. A. Acevedo Barroso, B. Clément, T. Li, D. Sluse, J. Wilde, A. Melo, A. Sonnenfeld, C. Tortora, T. T. Thai, M. Millon, C. Spiniello, A. Manjón-García , et al. (280 additional authors not shown)

Abstract: We present AstroVink, a vision transformer classifier designed for automated identification of strong lens candidates in Euclid imaging. We build upon the DINOv2 encoder, fine tuned to distinguish between lens and non-lens galaxies. Our base model, trained on simulated strong lens systems and labelled non lenses, recovers 88 of the 110 lens candidates within the top 500 ranked candidates, correspo… ▽ More We present AstroVink, a vision transformer classifier designed for automated identification of strong lens candidates in Euclid imaging. We build upon the DINOv2 encoder, fine tuned to distinguish between lens and non-lens galaxies. Our base model, trained on simulated strong lens systems and labelled non lenses, recovers 88 of the 110 lens candidates within the top 500 ranked candidates, corresponding to an inspection efficiency of one lens per 5.7 inspected objects in our test set. After the Q1 data release, which yielded about 500 lens candidates, we retrained the model using high confidence lens candidates and new negatives, initially flagged as potential lenses by other classifiers but rejected during visual inspection. The retrained network further improves performance, achieving recovery of all 110 systems within the same ranking and reducing the inspection effort to one lens per 4.5 inspected objects, demonstrating that incorporating real examples significantly enhances model generalisation. An analysis of training subsets revealed that the inclusion of realistic negative examples played a key role in this improvement. Finally, we applied the retrained model to the Q1 original selection of 1.08M targets, followed by a new round of Space Warps citizen science inspection and expert vetting, where we identified a total of eight Grade A and 26 Grade B new lens candidates. These results demonstrate that transformer based architectures can recover strong lens candidates with high efficiency in real Euclid data, while substantially reducing the number of candidates requiring visual inspection. △ Less

Submitted 23 April, 2026; originally announced April 2026.

Comments: 21 pages, 6 figures, 1 table,submitted to A&A journal, dataset available at https://zenodo.org/records/17425610, software available at https://github.com/SaamieVincken/AstroVink

Euclid Quick Data Release (Q1). AgileLens: A scalable CNN-based pipeline for strong gravitational lens identification

Authors: Euclid Collaboration, X. Xu, R. Chen, T. Li, A. R. Cooray, S. Schuldt, J. A. Acevedo Barroso, D. Stern, D. Scott, M. Meneghetti, G. Despali, J. Chopra, Y. Cao, M. Cheng, J. Buda, J. Zhang, J. Furumizo, R. Valencia, Z. Jiang, C. Tortora, N. E. P. Lines, T. E. Collett, S. Fotopoulou, A. Galan, A. Manjón-García , et al. (286 additional authors not shown)

Abstract: We present an end-to-end, iterative pipeline for efficient identification of strong galaxy--galaxy lensing systems, applied to the Euclid Q1 imaging data. Starting from VIS catalogues, we reject point sources, apply a magnitude cut (I$_E$ $\leq$ 24) on deflectors, and run a pixel-level artefact/noise filter to build 96 $\times$ 96 pix cutouts; VIS+NISP colour composites are constructed with a VIS-… ▽ More We present an end-to-end, iterative pipeline for efficient identification of strong galaxy--galaxy lensing systems, applied to the Euclid Q1 imaging data. Starting from VIS catalogues, we reject point sources, apply a magnitude cut (I$_E$ $\leq$ 24) on deflectors, and run a pixel-level artefact/noise filter to build 96 $\times$ 96 pix cutouts; VIS+NISP colour composites are constructed with a VIS-anchored luminance scheme that preserves VIS morphology and NISP colour contrast. A VIS-only seed classifier supplies clear positives and typical impostors, from which we curate a morphology-balanced negative set and augment scarce positives. Among the six CNNs studied initially, a modified VGG16 (GlobalAveragePooling + 256/128 dense layers with the last nine layers trainable) performs best; the training set grows from 27 seed lenses (augmented to 1809) plus 2000 negatives to a colour dataset of 30,686 images. After three rounds of iterative fine-tuning, human grading of the top 4000 candidates ranked by the final model yields 441 Grade A/B candidate lensing systems, including 311 overlapping with the existing Q1 strong-lens catalogue, and 130 additional A/B candidates (9 As and 121 Bs) not previously reported. Independently, the model recovers 740 out of 905 (81.8%) candidate Q1 lenses within its top 20,000 predictions, considering off-centred samples. Candidates span I$_E$ $\simeq$ 17--24 AB mag (median 21.3 AB mag) and are redder in Y$_E$--H$_E$ than the parent population, consistent with massive early-type deflectors. Each training iteration required a week for a small team, and the approach easily scales to future Euclid releases; future work will calibrate the selection function via lens injection, extend recall through uncertainty-aware active learning, explore multi-scale or attention-based neural networks with fast post-hoc vetters that incorporate lens models into the classification. △ Less

Submitted 7 April, 2026; originally announced April 2026.

Comments: 30 pages, 16 figures

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine F -- Bright and low-redshift strong lenses

Authors: Euclid Collaboration, L. R. Ecker, M. Fabricius, S. Seitz, R. Saglia, N. E. P. Lines, P. Holloway, T. Li, A. Verma, F. Balzer, Q. Jin, A. Manjón-García, S. H. Vincken, J. Wilde, J. A. Acevedo Barroso, J. W. Nightingale, K. Rojas, S. Schuldt, M. Walmsley, T. E. Collett, G. Despali, A. Sonnenfeld, C. Tortora, R. B. Metcalf, R. Bender , et al. (324 additional authors not shown)

Abstract: We present 72 additional galaxy-galaxy strong lenses that complement the sample discovered in the Euclid Quick Release 1 data (63.1 deg^2) of the Strong Lens Discovery Engine (SLDE) papers A-E. It is shown that previous pre-selection of potential lenses, which excluded objects from the Gaia catalogue, led to missing several bright and low-redshift strong lenses, adding more than 10% new strong len… ▽ More We present 72 additional galaxy-galaxy strong lenses that complement the sample discovered in the Euclid Quick Release 1 data (63.1 deg^2) of the Strong Lens Discovery Engine (SLDE) papers A-E. It is shown that previous pre-selection of potential lenses, which excluded objects from the Gaia catalogue, led to missing several bright and low-redshift strong lenses, adding more than 10% new strong lens candidates compared to the previous search. In total, the catalogue includes 38 "grade A" (confident) and 34 "grade B" (probable) candidates. These lenses are identified through a combination of two independent searches for bright nearby objects: one based on machine-learning models followed by expert visual inspection, and the other based solely on expert visual inspection, targeting objects not included in the initial machine-learning selection (a limitation identified only after extensive visual inspection). With these additional strong lens candidates, we augment the expected number of high-confidence candidates in the Euclid Wide Survey from previous forecasts to 120000. Detailed semi-automated lens modelling confirms at least 41 systems out of 72, a fraction consistent with that found in SLDE A (315 out of 488). These include: multiple edge-on disc lenses; sources with arcs near the lens centre; "red sources"; and an edge-on disk galaxy lensing a galaxy merger, producing two sets of lensed features, an Einstein ring and a doubly imaged component. The median redshift of these systems is $Δ$ z ~ 0.3 lower than that of the SLDE A sample. △ Less

Submitted 30 March, 2026; originally announced March 2026.

A Salpeter IMF and an NFW halo: Disentangling the dark and stellar mass of an elliptical galaxy through precise lens modelling of a double-source-plane system

Authors: Tian Li, Thomas E. Collett, Coleman M. Krawczyk, Giovanni Granata, Wolfgang J. R. Enzi, Daniel J. Ballard, Natalie E. P. Lines, Ana Sainz de Murieta, Luke Weisenbach, Dan Ryczanowski

Abstract: We present a strong lensing analysis of the double source plane lens J0946+1006 (colloquially "Jackpot" lens) to measure the inner dark matter density profile, the stellar-to-halo mass ratio, and the stellar initial mass function normalisation using a two component stellar plus dark matter mass model. The stellar mass follows a multi-Gaussian expansion light model with a free global mass-to-light… ▽ More We present a strong lensing analysis of the double source plane lens J0946+1006 (colloquially "Jackpot" lens) to measure the inner dark matter density profile, the stellar-to-halo mass ratio, and the stellar initial mass function normalisation using a two component stellar plus dark matter mass model. The stellar mass follows a multi-Gaussian expansion light model with a free global mass-to-light ratio and an allowed radial $M/L$ gradient, while the dark matter is described by an elliptical generalised NFW halo. The double-source-plane geometry provides additional leverage against the mass-sheet transformation and helps constrain the radial mass profile. Despite allowing both a radial stellar $M/L$ gradient and a generalised NFW halo, the data prefer the canonical picture: an approximately constant stellar mass-to-light ratio with a Salpeter-like IMF normalisation, and a dark matter halo consistent with NFW. We infer $M_{\star} = 4.4^{+0.25}_{-0.39}\times 10^{11}\,M_{\odot}$ and an inner halo slope $γ_{\rm in}^{\rm halo} = 1.04^{+0.10}_{-0.14}$. The halo mass is $M_{200}^{\rm halo} = 1.11^{+0.37}_{-0.32}\times 10^{13}\,M_{\odot}$, implying $\log_{10}(M_{200}/M_{\star})=1.41^{+0.13}_{-0.14}$. At fixed halo mass, the inferred stellar mass lies $\sim0.1$ dex above typical literature stellar halo mass relations at similar redshift, which is comparable to the intrinsic scatter of these relations. We expect this approach to provide a practical template for future dark matter studies with the large double-source-plane lens samples from Euclid. △ Less

Submitted 9 July, 2026; v1 submitted 24 February, 2026; originally announced February 2026.

Journal ref: Mon Not R Astron Soc (2026)

Multi-band Reconstruction of Sixteen Gravitational Lens Systems using PISCO data

Authors: Huimin Qu, Daniel J. Ballard, Geraint F. Lewis, Karl Glazebrook, Antony Stark, Sarah M. Sweet, Colin Jacobs, Kim-Vy Tran, Brian Stalder, Tania M. Barone, Tucker Jones, Keerthi Vasan G. C., Thomas E. Collett, Glenn G. Kacprzak, Dorota Bayer

Abstract: Next-generation surveys such as the Euclid survey, the Legacy Survey of Space and Time (LSST), and the China Space Station Telescope (CSST) survey are expected to discover ~10^5 galaxy-galaxy scale strong gravitational lenses. This motivates the development of scalable and robust lens modeling approaches that can efficiently and reliably learn from wide-field survey datasets before high-resolution… ▽ More Next-generation surveys such as the Euclid survey, the Legacy Survey of Space and Time (LSST), and the China Space Station Telescope (CSST) survey are expected to discover ~10^5 galaxy-galaxy scale strong gravitational lenses. This motivates the development of scalable and robust lens modeling approaches that can efficiently and reliably learn from wide-field survey datasets before high-resolution follow-up. We design a scalable, Bayesian, Lenstronomy-based pipeline and apply it to a sample of sixteen lens candidates observed with the Parallel Imager for Southern Cosmology Observations (PISCO) on the Magellan telescope. PISCO provides four-band imaging (z, i, r, g) with colours, depth and seeing conditions comparable to LSST. To fully exploit the constraining power of this dataset, our pipeline performs simultaneous multi-band modeling, using a common mass profile across all four bands while allowing independent light profiles in each. This approach leverages color information to provide joint constraints on the lens mass and yields reduced uncertainties compared to single-band analyses. Fifteen out of sixteen PISCO lens candidates are successfully recovered with interpretable lensing configurations, including DESJ0533-2536, the first reported hyperbolic-umbilic galaxy-galaxy scale strong lensing candidate. We further assess how much model complexity can be reliably constrained given the resolution and seeing of PISCO-like data. Overall, our results demonstrate that scalable, multi-band lens modeling of ground-based data can extract meaningful constraints on mass and source morphology, providing a practical pathway to maximize the scientific return from large samples in upcoming surveys. △ Less

Submitted 21 January, 2026; originally announced January 2026.

Comments: Accepted by MNRAS. 22 pages, 16 figures, 4 tables

Euclid Quick Data Release (Q1). From simulations to sky: Advancing machine-learning lens detection with real Euclid data

Authors: Euclid Collaboration, N. E. P. Lines, T. E. Collett, P. Holloway, K. Rojas, S. Schuldt, R. B. Metcalf, T. Li, A. Verma, G. Despali, F. Courbin, R. Gavazzi, C. Tortora, B. Clément, N. Aghanim, B. Altieri, L. Amendola, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano , et al. (279 additional authors not shown)

Abstract: In the era of large-scale surveys like Euclid, machine learning has become an essential tool for identifying rare yet scientifically valuable objects, such as strong gravitational lenses. However, supervised machine-learning approaches require large quantities of labelled examples to train on, and the limited number of known strong lenses has lead to a reliance on simulations for training. A well-… ▽ More In the era of large-scale surveys like Euclid, machine learning has become an essential tool for identifying rare yet scientifically valuable objects, such as strong gravitational lenses. However, supervised machine-learning approaches require large quantities of labelled examples to train on, and the limited number of known strong lenses has lead to a reliance on simulations for training. A well-known challenge is that machine-learning models trained on one data domain often underperform when applied to a different domain: in the context of lens finding, this means that strong performance on simulated lenses does not necessarily translate into equally good performance on real observations. In Euclid's Quick Data Release 1 (Q1), covering 63 deg2, 500 strong lens candidates were discovered through a synergy of machine learning, citizen science, and expert visual inspection. These discoveries now allow us to quantify this performance gap and investigate the impact of training on real data. We find that a network trained only on simulations recovers up to 92% of simulated lenses with 100% purity, but only achieves 50% completeness with 24% purity on real Euclid data. By augmenting training data with real Euclid lenses and non-lenses, completeness improves by 25-30% in terms of the expected yield of discoverable lenses in Euclid DR1 and the full Euclid Wide Survey. Roughly 20% of this improvement comes from the inclusion of real lenses in the training data, while 5-10% comes from exposure to a more diverse set of non-lenses and false-positives from Q1. We show that the most effective lens-finding strategy for real-world performance combines the diversity of simulations with the fidelity of real lenses. This hybrid approach establishes a clear methodology for maximising lens discoveries in future data releases from Euclid, and will likely also be applicable to other surveys such as LSST. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 16 pages

iPTF16geu through the lens of thermonuclear explosion models

Authors: Ana Sainz de Murieta, Mark R. Magee, Tian Li, Thomas E. Collett, Joel Johansson

Abstract: The magnification resulting from strong gravitational lensing is a powerful tool to add new constraints to the cosmic evolution of supernova progenitors by enabling the study of distant supernovae that would otherwise not be observable. iPTF16geu is the most well-observed gravitationally lensed supernova (glSN) to date. At a redshift of $z = 0.409$ and magnified by a factor of $\sim$68, extensive… ▽ More The magnification resulting from strong gravitational lensing is a powerful tool to add new constraints to the cosmic evolution of supernova progenitors by enabling the study of distant supernovae that would otherwise not be observable. iPTF16geu is the most well-observed gravitationally lensed supernova (glSN) to date. At a redshift of $z = 0.409$ and magnified by a factor of $\sim$68, extensive photometric and spectroscopic observations have been obtained. The explosion mechanism producing this rare event and differences compared to lower redshift supernovae however have not been explored in detail. Here we compare observations of iPTF16geu to existing radiative transfer simulations of type Ia supernova explosion models selected from the literature. We find that overall the DDC6, PDDEL1, and N10 models produce the closest match to the light curves and many absorption features, providing some evidence in favour of the delayed detonation scenario. All models struggle however to replicate the observed colours and in particular the rest-frame UV. We also investigate the magnification and reddening values required to improve agreement with the selected models. Upcoming surveys will significantly increase the samples of SNe discovered at high redshifts due to strong gravitational lensing. These glSNe will enable tighter constraints on the explosion physics of type Ia supernovae and how this has evolved throughout the Universe. △ Less

Submitted 13 January, 2026; v1 submitted 1 October, 2025; originally announced October 2025.

Comments: MNRAS. 16 pages, 12 figures

Journal ref: Mon Not R Astron Soc (2026)

Lensed stars in galaxy-galaxy strong lensing -- a JWST prediction for the Cosmic Horseshoe

Authors: Sung Kei Li, Luke Weisenbach, Thomas E. Collett, Jose M. Diego, Jeremy Lim, Thomas J. Broadhurst, Alex Chow, Wolfgang J. R. Enzi, Patrick L. Kelly, Carlos R. Melo-Carneiro, Jose M. Palencia, Liliya L. R. Williams, Jiashuo Zhang

Abstract: We explore for the first time the possibility of detecting lensed star transients in galaxy-galaxy strong lensing systems upon repeated, deep imaging using the {\it James-Webb Space Telescope} ({\it JWST}). Our calculation predicts that the extremely high recent star formation rate of $\sim 140\,M_{\odot}\textrm{yr}^{-1}$ over the last 50 Myr (not accounting for image multiplicity) in the ``Cosmic… ▽ More We explore for the first time the possibility of detecting lensed star transients in galaxy-galaxy strong lensing systems upon repeated, deep imaging using the {\it James-Webb Space Telescope} ({\it JWST}). Our calculation predicts that the extremely high recent star formation rate of $\sim 140\,M_{\odot}\textrm{yr}^{-1}$ over the last 50 Myr (not accounting for image multiplicity) in the ``Cosmic Horseshoe'' lensed system ($z = 2.381$) generates many young, bright stars, of which their large abundance is expected to lead to a detection rate of $\sim 60$ transients per pointing in {\it JWST} observations with a $5σ$ limiting magnitude of $\sim 29\,m_{AB}$. With the high expected detection rate and little room for uncertainty for the lens model compared with cluster lenses, our result suggests that the Cosmic Horseshoe could be an excellent tool to test the nature of dark matter based on the spatial distribution of transients, and can be used to constrain axion mass if dark matter is constituted of ultra-light axions. We also argue that the large distance modulus of $\sim46.5\,$mag at $z \approx 2.4$ can act as a filter to screen out less massive stars as transients and allow one to better constrain the high-mass end of the stellar initial mass function based on the transient detection rate. Follow-up {\it JWST} observations of the Cosmic Horseshoe would allow one to better probe the nature of dark matter and the star formation properties, such as the initial mass function at the cosmic noon, via lensed star transients. △ Less

Submitted 9 April, 2026; v1 submitted 19 September, 2025; originally announced September 2025.

Comments: 13 pages, 13 figures, Published in MNRAS

Journal ref: Mon Not R Astron Soc (2025) 4469-4481

Constraining Cosmology with Double-source-plane Strong Gravitational Lenses from the AGEL Survey

Authors: Duncan J. Bowden, Nandini Sahu, Anowar J. Shajib, Kim-Vy Tran, Tania M. Barone, Keerthi Vasan G. C., Daniel J. Ballard, Thomas E. Collett, Faith Dalessandro, Giovanni Ferrami, Karl Glazebrook, William J. Gottemoller, Leena Iwamoto, Tucker Jones, Glenn G. Kacprzak, Geraint F. Lewis, Haven McIntosh-Lombardo, Hannah Skobe, Sherry H. Suyu, Sarah M. Sweet

Abstract: Double-source-plane strong gravitational lenses (DSPLs), with two sources at different redshifts, are independent cosmological probes of the dark energy equation of state parameter $w$ and the matter density parameter $Ω_{\rm m}$. We present the lens model for the DSPL AGEL035346$-$170639 and infer cosmological constraints from this system for flat $Λ$ cold dark matter and flat $w$CDM cosmologies.… ▽ More Double-source-plane strong gravitational lenses (DSPLs), with two sources at different redshifts, are independent cosmological probes of the dark energy equation of state parameter $w$ and the matter density parameter $Ω_{\rm m}$. We present the lens model for the DSPL AGEL035346$-$170639 and infer cosmological constraints from this system for flat $Λ$ cold dark matter and flat $w$CDM cosmologies. From the joint posterior of $w$ and $Ω_{\rm m}$ in the flat $w$CDM cosmology, we extract the following median values and 1$σ$ uncertainties: $w = -1.52^{+0.49}_{-0.33}$ and $Ω_{\rm m} = 0.192^{+0.305}_{-0.131}$ from AGEL0353 alone. Combining our measurements with two previously analyzed DSPLs, we present the joint constraint on these parameters from a sample of three, the largest galaxy-scale DSPL sample used for cosmological measurement to date. The combined precision of $w$ from three DSPLs is higher by 15% over AGEL0353 alone. Combining DSPL and cosmic microwave background (CMB) measurements improves the precision of $w$ from CMB-only constraints by 39%, demonstrating the complementarity of DSPLs with the CMB. Despite their promising constraining power, DSPLs are limited by sample size, with only a handful discovered so far. Although ongoing and near-future wide-area sky surveys will increase the number of known DSPLs by up to two orders of magnitude, these systems will still require dedicated high-resolution imaging and spectroscopic follow-ups like those presented in this paper. Our ASTRO 3D Galaxy Evolution with Lenses collaboration is undertaking such follow-up campaigns for several newly discovered DSPLs and will provide cosmological measurements from larger samples of DSPLs in the future. △ Less

Submitted 4 November, 2025; v1 submitted 18 September, 2025; originally announced September 2025.

Comments: 14 pages, 10 figures, Updated final version published in the Astrophysical Journal (ApJ)

Journal ref: Duncan J. Bowden et al 2025 ApJ 993 124

The revolution in strong lensing discoveries from Euclid

Authors: Natalie E. P. Lines, Tian Li, Thomas E. Collett, Philip Holloway, James W. Nightingale, Karina Rojas, Aprajita Verma, Mike Walmsley

Abstract: Strong gravitational lensing offers a powerful and direct probe of dark matter, galaxy evolution and cosmology, yet strong lenses are rare: only 1 in roughly 10,000 massive galaxies can lens a background source into multiple images. The European Space Agency's Euclid telescope, with its unique combination of high-resolution imaging and wide-area sky coverage, is set to transform this field. In its… ▽ More Strong gravitational lensing offers a powerful and direct probe of dark matter, galaxy evolution and cosmology, yet strong lenses are rare: only 1 in roughly 10,000 massive galaxies can lens a background source into multiple images. The European Space Agency's Euclid telescope, with its unique combination of high-resolution imaging and wide-area sky coverage, is set to transform this field. In its first quick data release, covering just 0.45% of the full survey area, around 500 high-quality strong lens candidates have been identified using a synergy of machine learning, citizen science and expert visual inspection. This dataset includes exotic systems such as compound lenses and edge-on disk lenses, demonstrating Euclid's capacity to probe the lens parameter space. The machine learning models developed to discover strong lenses in Euclid data are able to find lenses with high purity rates, confirming that the mission's forecast of discovering over 100,000 strong lenses is achievable during its 6-year mission. This will increase the number of known strong lenses by two orders of magnitude, transforming the science that can be done with strong lensing. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Comments: Published in Nature Astronomy. This version of the article has been accepted for publication but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1038/s41550-025-02616-5

Cosmography with the Double Source Plane Strong Gravitational Lens AGEL150745+052256

Authors: Nandini Sahu, Anowar J. Shajib, Kim-Vy Tran, Hannah Skobe, Sunny Rhoades, Tucker Jones, Karl Glazebrook, Thomas E. Collett, Sherry H. Suyu, Tania M. Barone, Keerthi Vasan G. C., Duncan J. Bowden, Daniel Ballard, Glenn G. Kacprzak, Sarah M. Sweet, Geraint F. Lewis, Themiya Nanayakkara

Abstract: Strong gravitational lenses with two background sources at widely separated redshifts are a powerful and independent probe of cosmological parameters. We can use these systems, known as Double-Source-Plane Lenses (DSPLs), to measure the ratio ($β$) of angular-diameter distances of the sources, which is sensitive to the matter density ($Ω_m$) and the equation-of-state parameter for dark-energy (… ▽ More Strong gravitational lenses with two background sources at widely separated redshifts are a powerful and independent probe of cosmological parameters. We can use these systems, known as Double-Source-Plane Lenses (DSPLs), to measure the ratio ($β$) of angular-diameter distances of the sources, which is sensitive to the matter density ($Ω_m$) and the equation-of-state parameter for dark-energy ($w$). However, DSPLs are rare and require high-resolution imaging and spectroscopy for detection, lens modeling, and measuring $β$. Here we report only the second DSPL ever used to measure cosmological parameters. We model the DSPL AGEL150745+052256 from the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey using HST/WFC3 imaging and Keck/KCWI spectroscopy. The spectroscopic redshifts for the deflector and two sources in AGEL1507 are $z_{\rm defl}=0.594$, $z_{\rm S1}=2.163$, and $z_{\rm S2}=2.591$. We measure a stellar velocity dispersion of $σ_{\rm obs}=109 \pm 27$ km s$^{-1}$ for the nearer source. Using $σ_{\rm obs}$ for the main deflector (from literature) and S1, we test the robustness of our DSPL model. We measure $β=0.953^{+0.008}_{-0.010}$ for AGEL1507 and infer $Ω_{\rm m}=0.33^{+0.38}_{-0.23}$ for $Λ$CDM cosmology. Combining AGEL1507 with the published model of the Jackpot lens improves the precision on $Ω_{\rm m}$ ($Λ$CDM) and w (wCDM) by $\sim 10 \%$. The inclusion of DSPLs significantly improves the constraints when combined with Plancks cosmic microwave background observations, enhancing precision on w by $30 \%$. This paper demonstrates the constraining power of DSPLs and their complementarity to other standard cosmological probes. Tighter future constraints from larger DSPL samples discovered from ongoing and forthcoming large-area sky surveys would provide insights into the nature of dark energy. △ Less

Submitted 1 April, 2025; originally announced April 2025.

Comments: 19 pages, 10 figures, Submitted for publication to the Astrophysical Journal (ApJ)

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine E -- Ensemble classification of strong gravitational lenses: lessons for Data Release 1

Authors: Euclid Collaboration, P. Holloway, A. Verma, M. Walmsley, P. J. Marshall, A. More, T. E. Collett, N. E. P. Lines, L. Leuzzi, A. Manjón-García, S. H. Vincken, J. Wilde, R. Pearce-Casey, I. T. Andika, J. A. Acevedo Barroso, T. Li, A. Melo, R. B. Metcalf, K. Rojas, B. Clément, H. Degaudenzi, F. Courbin, G. Despali, R. Gavazzi, S. Schuldt , et al. (321 additional authors not shown)

Abstract: The Euclid Wide Survey (EWS) is expected to identify of order $100\,000$ galaxy-galaxy strong lenses across $14\,000$deg$^2$. The Euclid Quick Data Release (Q1) of $63.1$deg$^2$ Euclid images provides an excellent opportunity to test our lens-finding ability, and to verify the anticipated lens frequency in the EWS. Following the Q1 data release, eight machine learning networks from five teams were… ▽ More The Euclid Wide Survey (EWS) is expected to identify of order $100\,000$ galaxy-galaxy strong lenses across $14\,000$deg$^2$. The Euclid Quick Data Release (Q1) of $63.1$deg$^2$ Euclid images provides an excellent opportunity to test our lens-finding ability, and to verify the anticipated lens frequency in the EWS. Following the Q1 data release, eight machine learning networks from five teams were applied to approximately one million images. This was followed by a citizen science inspection of a subset of around $100\,000$ images, of which $65\%$ received high network scores, with the remainder randomly selected. The top scoring outputs were inspected by experts to establish confident (grade A), likely (grade B), possible (grade C), and unlikely lenses. In this paper we combine the citizen science and machine learning classifiers into an ensemble, demonstrating that a combined approach can produce a purer and more complete sample than the original individual classifiers. Using the expert-graded subset as ground truth, we find that this ensemble can provide a purity of $52\pm2\%$ (grade A/B lenses) with $50\%$ completeness (for context, due to the rarity of lenses a random classifier would have a purity of $0.05\%$). We discuss future lessons for the first major Euclid data release (DR1), where the big-data challenges will become more significant and will require analysing more than $\sim300$ million galaxies, and thus time investment of both experts and citizens must be carefully managed. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Comments: Paper submitted as part of the A&A Special Issue `Euclid Quick Data Release (Q1)', 15 pages, 8 figures

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine D -- Double-source-plane lens candidates

Authors: Euclid Collaboration, T. Li, T. E. Collett, M. Walmsley, N. E. P. Lines, K. Rojas, J. W. Nightingale, W. J. R. Enzi, L. A. Moustakas, C. Krawczyk, R. Gavazzi, G. Despali, P. Holloway, S. Schuldt, F. Courbin, R. B. Metcalf, D. J. Ballard, A. Verma, B. Clément, H. Degaudenzi, A. Melo, J. A. Acevedo Barroso, L. Leuzzi, A. Manjón-García, R. Pearce-Casey , et al. (313 additional authors not shown)

Abstract: Strong gravitational lensing systems with multiple source planes are powerful tools for probing the density profiles and dark matter substructure of the galaxies. The ratio of Einstein radii is related to the dark energy equation of state through the cosmological scaling factor $β$. However, galaxy-scale double-source-plane lenses (DSPLs) are extremely rare. In this paper, we report the discovery… ▽ More Strong gravitational lensing systems with multiple source planes are powerful tools for probing the density profiles and dark matter substructure of the galaxies. The ratio of Einstein radii is related to the dark energy equation of state through the cosmological scaling factor $β$. However, galaxy-scale double-source-plane lenses (DSPLs) are extremely rare. In this paper, we report the discovery of four new galaxy-scale double-source-plane lens candidates in the Euclid Quick Release 1 (Q1) data. These systems were initially identified through a combination of machine learning lens-finding models and subsequent visual inspection from citizens and experts. We apply the widely-used {\tt LensPop} lens forecasting model to predict that the full \Euclid survey will discover 1700 DSPLs, which scales to $6 \pm 3$ DSPLs in 63 deg$^2$, the area of Q1. The number of discoveries in this work is broadly consistent with this forecast. We present lens models for each DSPL and infer their $β$ values. Our initial Q1 sample demonstrates the promise of \Euclid to discover such rare objects. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Comments: Paper submitted as part of the A&A Special Issue `Euclid Quick Data Release (Q1), 16 pages, 11 figures

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine C: Finding lenses with machine learning

Authors: Euclid Collaboration, N. E. P. Lines, T. E. Collett, M. Walmsley, K. Rojas, T. Li, L. Leuzzi, A. Manjón-García, S. H. Vincken, J. Wilde, P. Holloway, A. Verma, R. B. Metcalf, I. T. Andika, A. Melo, M. Melchior, H. Domínguez Sánchez, A. Díaz-Sánchez, J. A. Acevedo Barroso, B. Clément, C. Krawczyk, R. Pearce-Casey, S. Serjeant, F. Courbin, G. Despali , et al. (328 additional authors not shown)

Abstract: Strong gravitational lensing has the potential to provide a powerful probe of astrophysics and cosmology, but fewer than 1000 strong lenses have been confirmed so far. With a 0.16'' resolution covering a third of the sky, the Euclid telescope will revolutionise the identification of strong lenses, with 170 000 lenses forecasted to be discovered amongst the 1.5 billion galaxies it will observe. We… ▽ More Strong gravitational lensing has the potential to provide a powerful probe of astrophysics and cosmology, but fewer than 1000 strong lenses have been confirmed so far. With a 0.16'' resolution covering a third of the sky, the Euclid telescope will revolutionise the identification of strong lenses, with 170 000 lenses forecasted to be discovered amongst the 1.5 billion galaxies it will observe. We present an analysis of the performance of five machine-learning models at finding strong gravitational lenses in the quick release of Euclid data (Q1) covering 63 deg2. The models have been validated by citizen scientists and expert visual inspection. We focus on the best-performing network: a fine-tuned version of the Zoobot pretrained model originally trained to classify galaxy morphologies in heterogeneous astronomical imaging surveys. Of the one million Q1 objects that Zoobot was tasked to find strong lenses within, the top 1000 ranked objects contain 122 grade A lenses (almost-certain lenses) and 41 grade B lenses (probable lenses). A deeper search with the five networks combined with visual inspection yielded 250 (247) grade A (B) lenses, of which 224 (182) are ranked in the top 20 000 by Zoobot. When extrapolated to the full Euclid survey, the highest ranked one million images will contain 75 000 grade A or B strong gravitational lenses. △ Less

Submitted 26 June, 2025; v1 submitted 19 March, 2025; originally announced March 2025.

Comments: Paper accepted for the A&A Special Issue `Euclid Quick Data Release (Q1)', 24 pages

Euclid Quick Data Release (Q1) The Strong Lensing Discovery Engine B -- Early strong lens candidates from visual inspection of high velocity dispersion galaxies

Authors: Euclid Collaboration, K. Rojas, T. E. Collett, J. A. Acevedo Barroso, J. W. Nightingale, D. Stern, L. A. Moustakas, S. Schuldt, G. Despali, A. Melo, M. Walmsley, D. J. Ballard, W. J. R. Enzi, T. Li, A. Sainz de Murieta, I. T. Andika, B. Clément, F. Courbin, L. R. Ecker, R. Gavazzi, N. Jackson, A. Kovács, P. Matavulj, M. Meneghetti, S. Serjeant , et al. (314 additional authors not shown)

Abstract: We present a search for strong gravitational lenses in Euclid imaging with high stellar velocity dispersion ($σ_ν> 180$ km/s) reported by SDSS and DESI. We performed expert visual inspection and classification of $11\,660$ \Euclid images. We discovered 38 grade A and 40 grade B candidate lenses, consistent with an expected sample of $\sim$32. Palomar spectroscopy confirmed 5 lens systems, while DE… ▽ More We present a search for strong gravitational lenses in Euclid imaging with high stellar velocity dispersion ($σ_ν> 180$ km/s) reported by SDSS and DESI. We performed expert visual inspection and classification of $11\,660$ \Euclid images. We discovered 38 grade A and 40 grade B candidate lenses, consistent with an expected sample of $\sim$32. Palomar spectroscopy confirmed 5 lens systems, while DESI spectra confirmed one, provided ambiguous results for another, and help to discard one. The \Euclid automated lens modeler modelled 53 candidates, confirming 38 as lenses, failing to model 9, and ruling out 6 grade B candidates. For the remaining 25 candidates we could not gather additional information. More importantly, our expert-classified non-lenses provide an excellent training set for machine learning lens classifiers. We create high-fidelity simulations of \Euclid lenses by painting realistic lensed sources behind the expert tagged (non-lens) luminous red galaxies. This training set is the foundation stone for the \Euclid galaxy-galaxy strong lensing discovery engine. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Comments: Paper submitted as part of the A&A Special Issue `Euclid Quick Data Release (Q1)', 18 pages, 9 figures

Euclid Quick Data Release (Q1): The Strong Lensing Discovery Engine A -- System overview and lens catalogue

Authors: Euclid Collaboration, M. Walmsley, P. Holloway, N. E. P. Lines, K. Rojas, T. E. Collett, A. Verma, T. Li, J. W. Nightingale, G. Despali, S. Schuldt, R. Gavazzi, A. Melo, R. B. Metcalf, I. T. Andika, L. Leuzzi, A. Manjón-García, R. Pearce-Casey, S. H. Vincken, J. Wilde, V. Busillo, C. Tortora, J. A. Acevedo Barroso, H. Dole, L. R. Ecker , et al. (350 additional authors not shown)

Abstract: We present a catalogue of 497 galaxy-galaxy strong lenses in the Euclid Quick Release 1 data (63 deg$^2$). In the initial 0.45\% of Euclid's surveys, we double the total number of known lens candidates with space-based imaging. Our catalogue includes 250 grade A candidates, the vast majority of which (243) were previously unpublished. Euclid's resolution reveals rare lens configurations of scienti… ▽ More We present a catalogue of 497 galaxy-galaxy strong lenses in the Euclid Quick Release 1 data (63 deg$^2$). In the initial 0.45\% of Euclid's surveys, we double the total number of known lens candidates with space-based imaging. Our catalogue includes 250 grade A candidates, the vast majority of which (243) were previously unpublished. Euclid's resolution reveals rare lens configurations of scientific value including double-source-plane lenses, edge-on lenses, complete Einstein rings, and quadruply-imaged lenses. We resolve lenses with small Einstein radii ($θ_{\rm E} < 1''$) in large numbers for the first time. These lenses are found through an initial sweep by deep learning models, followed by Space Warps citizen scientist inspection, expert vetting, and system-by-system modelling. Our search approach scales straightforwardly to Euclid Data Release 1 and, without changes, would yield approximately 7000 high-confidence (grade A or B) lens candidates by late 2026. Further extrapolating to the complete Euclid Wide Survey implies a likely yield of over 100000 high-confidence candidates, transforming strong lensing science. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Comments: Data: https://doi.org/10.5281/zenodo.15003116. Paper submitted as part of the A&A Special Issue `Euclid Quick Data Release (Q1)'. 20 pages, 11 figures, plus appendices

The La Silla Schmidt Southern Survey

Authors: Adam A. Miller, Natasha S. Abrams, Greg Aldering, Shreya Anand, Charlotte R. Angus, Iair Arcavi, Charles Baltay, Franz E. Bauer, Daniel Brethauer, Joshua S. Bloom, Hemanth Bommireddy, Marcio Catelan, Ryan Chornock, Peter Clark, Thomas E. Collett, Georgios Dimitriadis, Sara Faris, Francisco Forster, Anna Franckowiak, Christopher Frohmaier, Lluıs Galbany, Renato B. Galleguillos, Ariel Goobar, Claudia P. Gutierrez, Saarah Hall , et al. (53 additional authors not shown)

Abstract: We present the La Silla Schmidt Southern Survey (LS4), a new wide-field, time-domain survey to be conducted with the 1 m ESO Schmidt telescope. The 268 megapixel LS4 camera mosaics 32 2k$\times$4k fully depleted CCDs, providing a $\sim$20 deg$^2$ field of view with $1''$ pixel$^{-1}$ resolution. The LS4 camera will have excellent performance at longer wavelengths: in a standard 45 s exposure the e… ▽ More We present the La Silla Schmidt Southern Survey (LS4), a new wide-field, time-domain survey to be conducted with the 1 m ESO Schmidt telescope. The 268 megapixel LS4 camera mosaics 32 2k$\times$4k fully depleted CCDs, providing a $\sim$20 deg$^2$ field of view with $1''$ pixel$^{-1}$ resolution. The LS4 camera will have excellent performance at longer wavelengths: in a standard 45 s exposure the expected 5$σ$ limiting magnitudes in $g$, $i$, $z$ are $\sim$21.5, $\sim$20.9, and $\sim$20.3 mag (AB), respectively. The telescope design requires a novel filter holder that fixes different bandpasses over each quadrant of the detector. Two quadrants will have $i$ band, while the other two will be $g$ and $z$ band and color information will be obtained by dithering targets across the different quadrants. The majority (90%) of the observing time will be used to conduct a public survey that monitors the extragalactic sky at both moderate (3 d) and high (1 d) cadence, as well as focused observations within the Galactic bulge and plane. Alerts from the public survey will be broadcast to the community via established alert brokers. LS4 will run concurrently with the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). The combination of LS4+LSST will enable detailed holistic monitoring of many nearby transients: high-cadence LS4 observations will resolve the initial rise and peak of the light curve while less-frequent but deeper observations by LSST will characterize the years before and after explosion. Here, we summarize the primary science objectives of LS4 including microlensing events in the Galaxy, extragalactic transients, the search for electromagnetic counterparts to multi-messenger events, and cosmology. △ Less

Submitted 18 March, 2025; originally announced March 2025.

Comments: (to be submitted to PASP)

The AGEL Survey Data Release 2: A Gravitational Lens Sample for Galaxy Evolution and Cosmology

Authors: Tania M. Barone, Keerthi Vasan G. C., Kim-Vy Tran, Glenn G. Kacprzak, Karl Glazebrook, Tucker Jones, Duncan J. Bowden, Faith Dalessandro, Nandini Sahu, Hannah Skobe, Rebecca J. Allen, A. Makai Baker, Daniel J. Ballard, Yuguang Chen, Thomas E. Collett, Giovanni Ferrami, Jimena Gonzalez, William Gottemoller, Anishya Harshan, Xiaosheng Huang, Leena Iwamoto, Colin Jacobs, Tesla E. Jeltema, Kaustubh Rajesh Gupta, Geraint F. Lewis , et al. (9 additional authors not shown)

Abstract: The ASTRO 3D Galaxy Evolution with Lenses (AGEL) Survey is an ongoing effort to spectroscopically confirm a diverse sample of gravitational lenses with high spatial resolution imaging, to facilitate a broad range of science outcomes. The AGEL systems span single galaxy-scale deflectors to groups and clusters, and include rare targets such as galaxy-scale lenses with multiple sources, lensed quiesc… ▽ More The ASTRO 3D Galaxy Evolution with Lenses (AGEL) Survey is an ongoing effort to spectroscopically confirm a diverse sample of gravitational lenses with high spatial resolution imaging, to facilitate a broad range of science outcomes. The AGEL systems span single galaxy-scale deflectors to groups and clusters, and include rare targets such as galaxy-scale lenses with multiple sources, lensed quiescent galaxies, and Einstein rings. We build on the 77 systems presented in Tran et al. 2022 (AGEL data release 1) to present a total 138 lenses, and high resolution F140W and F200LP Hubble Space Telescope images for 71 lenses from a completed HST SNAP program. Lens candidates were originally identified by convolutional neural networks in the DES and DECaLS imaging fields, and of the targets with follow-up spectroscopy we find a high (96%) success rate. Compared with other spectroscopic lens samples, AGEL lenses tend to have both higher redshift deflectors and sources. We briefly discuss the common causes of false-positive candidates, and strategies for mitigating false-positives in next generation lens searches. Lastly, we present 6 galaxy-scale double-source plane lenses useful for cosmological analyses. With next-generation telescopes and surveys such as Euclid, Vera Rubin's Legacy Survey of Space and Time, Keck Observatory's KAPA program, and 4MOST's 4SLSLS surveys on the horizon, the AGEL survey represents a pathfinder for refining automated candidate search methods and identifying and triaging candidates for followup based on scientific potential. △ Less

Submitted 11 March, 2025; originally announced March 2025.

Comments: Submitted to AJ. 14 figures, 5 tables

Unveiling a 36 Billion Solar Mass Black Hole at the Centre of the Cosmic Horseshoe Gravitational Lens

Authors: Carlos R. Melo-Carneiro, Thomas E. Collett, Lindsay J. Oldham, Wolfgang J. R. Enzi, Cristina Furlanetto, Ana L. Chies-Santos, Tian Li

Abstract: Supermassive black holes (SMBHs) are found at the centre of every massive galaxy, with their masses tightly connected to their host galaxies through a co-evolution over cosmic time. For massive ellipticals, the SMBH mass ($M_\text{BH}$) strongly correlates with the central stellar velocity dispersion ($σ_e$), via the $M_\text{BH}-σ_e$ relation. However, SMBH mass measurements have traditionally re… ▽ More Supermassive black holes (SMBHs) are found at the centre of every massive galaxy, with their masses tightly connected to their host galaxies through a co-evolution over cosmic time. For massive ellipticals, the SMBH mass ($M_\text{BH}$) strongly correlates with the central stellar velocity dispersion ($σ_e$), via the $M_\text{BH}-σ_e$ relation. However, SMBH mass measurements have traditionally relied on central stellar dynamics in nearby galaxies ($z < 0.1$), limiting our ability to explore the SMBHs across cosmic time. In this work, we present a self-consistent analysis combining 2D stellar dynamics and lens modelling of the Cosmic Horseshoe gravitational lens system ($z = 0.44$), one of the most massive galaxies ever observed. Using integral-field spectroscopic data from MUSE and high-resolution imaging from HST, we model the radial arc and stellar kinematics, constraining the galaxy's central mass distribution and SMBH mass. Bayesian model comparison yields a $5σ$ detection of an ultramassive black hole (UMBH) with $\log_{10}(M_\text{BH}/M_{\odot}) = 10.56^{+0.07}_{-0.08} \pm (0.12)^\text{sys}$, consistent across various systematic tests. Our findings place the Cosmic Horseshoe $\sim$$1.5σ$ above the $M_\text{BH}-σ_e$ relation, supporting an emerging trend observed in BGCs and other massive galaxies. This suggests a steeper $M_\text{BH}-σ_e$ relationship at the highest masses, potentially driven by a different co-evolution of SMBHs and their host galaxies. Future surveys will uncover more radial arcs, enabling the detection of SMBHs over a broader redshift and mass range. These discoveries will further refine our understanding of the $M_\text{BH}-σ_e$ relation and its evolution across cosmic time. △ Less

Submitted 11 July, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 20 pages, 12 figures, 8 tables. Accepted for publication at MNRAS

Journal ref: Mon Not R Astron Soc (2025) 2853-2871

Euclid: Finding strong gravitational lenses in the Early Release Observations using convolutional neural networks

Authors: B. C. Nagam, J. A. Acevedo Barroso, J. Wilde, I. T. Andika, A. Manjón-García, R. Pearce-Casey, D. Stern, J. W. Nightingale, L. A. Moustakas, K. McCarthy, E. Moravec, L. Leuzzi, K. Rojas, S. Serjeant, T. E. Collett, P. Matavulj, M. Walmsley, B. Clément, C. Tortora, R. Gavazzi, R. B. Metcalf, C. M. O'Riordan, G. Verdoes Kleijn, L. V. E. Koopmans, E. A. Valentijn , et al. (170 additional authors not shown)

Abstract: The Early Release Observations (ERO) from Euclid have detected several new galaxy-galaxy strong gravitational lenses, with the all-sky survey expected to find 170,000 new systems, greatly enhancing studies of dark matter, dark energy, and constraints on the cosmological parameters. As a first step, visual inspection of all galaxies in one of the ERO fields (Perseus) was carried out to identify can… ▽ More The Early Release Observations (ERO) from Euclid have detected several new galaxy-galaxy strong gravitational lenses, with the all-sky survey expected to find 170,000 new systems, greatly enhancing studies of dark matter, dark energy, and constraints on the cosmological parameters. As a first step, visual inspection of all galaxies in one of the ERO fields (Perseus) was carried out to identify candidate strong lensing systems and compared to the predictions from Convolutional Neural Networks (CNNs). However, the entire ERO data set is too large for expert visual inspection. In this paper, we therefore extend the CNN analysis to the whole ERO data set, using different CNN architectures and methodologies. Using five CNN architectures, we identified 8,469 strong gravitational lens candidates from IE-band cutouts of 13 Euclid ERO fields, narrowing them to 97 through visual inspection, including 14 grade A and 31 grade B candidates. We present the spectroscopic confirmation of a strong gravitational lensing candidate, EUCLJ081705.61+702348.8. The foreground lensing galaxy, an early-type system at redshift z = 0.335, and the background source, a star-forming galaxy at redshift z = 1.475 with [O II] emission, are both identified. Lens modeling using the Euclid strong lens modeling pipeline reveals two distinct arcs in a lensing configuration, with an Einstein radius of 1.18 \pm 0.03 arcseconds, confirming the lensing nature of the system. These findings highlight the importance of a broad CNN search to efficiently reduce candidates, followed by visual inspection to eliminate false positives and achieve a high-purity sample of strong lenses in Euclid. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Euclid: A complete Einstein ring in NGC 6505

Authors: C. M. O'Riordan, L. J. Oldham, A. Nersesian, T. Li, T. E. Collett, D. Sluse, B. Altieri, B. Clément, K. Vasan G. C., S. Rhoades, Y. Chen, T. Jones, C. Adami, R. Gavazzi, S. Vegetti, D. M. Powell, J. A. Acevedo Barroso, I. T. Andika, R. Bhatawdekar, A. R. Cooray, G. Despali, J. M. Diego, L. R. Ecker, A. Galan, P. Gómez-Alvarez , et al. (173 additional authors not shown)

Abstract: We report the discovery of a complete Einstein ring around the elliptical galaxy NGC 6505, at $z=0.042$. This is the first strong gravitational lens discovered in Euclid and the first in an NGC object from any survey. The combination of the low redshift of the lens galaxy, the brightness of the source galaxy ($I_\mathrm{E}=18.1$ lensed, $I_\mathrm{E}=21.3$ unlensed), and the completeness of the ri… ▽ More We report the discovery of a complete Einstein ring around the elliptical galaxy NGC 6505, at $z=0.042$. This is the first strong gravitational lens discovered in Euclid and the first in an NGC object from any survey. The combination of the low redshift of the lens galaxy, the brightness of the source galaxy ($I_\mathrm{E}=18.1$ lensed, $I_\mathrm{E}=21.3$ unlensed), and the completeness of the ring make this an exceptionally rare strong lens, unidentified until its observation by Euclid. We present deep imaging data of the lens from the Euclid Visible Camera (VIS) and Near-Infrared Spectrometer and Photometer (NISP) instruments, as well as resolved spectroscopy from the Keck Cosmic Web Imager (KCWI). The Euclid imaging in particular presents one of the highest signal-to-noise ratio optical/near-infrared observations of a strong gravitational lens to date. From the KCWI data we measure a source redshift of $z=0.406$. Using data from the Dark Energy Spectroscopic Instrument (DESI) we measure a velocity dispersion for the lens galaxy of $σ_\star=303\pm15\,\mathrm{kms}^{-1}$. We model the lens galaxy light in detail, revealing angular structure that varies inside the Einstein ring. After subtracting this light model from the VIS observation, we model the strongly lensed images, finding an Einstein radius of 2.5 arcsec, corresponding to $2.1\,\mathrm{kpc}$ at the redshift of the lens. This is small compared to the effective radius of the galaxy, $R_\mathrm{eff}\sim 12.3\,\mathrm{arcsec}$. Combining the strong lensing measurements with analysis of the spectroscopic data we estimate a dark matter fraction inside the Einstein radius of $f_\mathrm{DM} = (11.1_{-3.5}^{+5.4})\%$ and a stellar initial mass-function (IMF) mismatch parameter of $α_\mathrm{IMF} = 1.26_{-0.08}^{+0.05}$, indicating a heavier-than-Chabrier IMF in the centre of the galaxy. △ Less

Submitted 10 February, 2025; originally announced February 2025.

Comments: Accepted in A&A. Press release: https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_discovers_a_stunning_Einstein_ring

Journal ref: A&A, 694, A145 (2025)

Euclid: Searches for strong gravitational lenses using convolutional neural nets in Early Release Observations of the Perseus field

Authors: R. Pearce-Casey, B. C. Nagam, J. Wilde, V. Busillo, L. Ulivi, I. T. Andika, A. Manjón-García, L. Leuzzi, P. Matavulj, S. Serjeant, M. Walmsley, J. A. Acevedo Barroso, C. M. O'Riordan, B. Clément, C. Tortora, T. E. Collett, F. Courbin, R. Gavazzi, R. B. Metcalf, R. Cabanac, H. M. Courtois, J. Crook-Mansour, L. Delchambre, G. Despali, L. R. Ecker , et al. (182 additional authors not shown)

Abstract: The Euclid Wide Survey (EWS) is predicted to find approximately 170 000 galaxy-galaxy strong lenses from its lifetime observation of 14 000 deg^2 of the sky. Detecting this many lenses by visual inspection with professional astronomers and citizen scientists alone is infeasible. Machine learning algorithms, particularly convolutional neural networks (CNNs), have been used as an automated method of… ▽ More The Euclid Wide Survey (EWS) is predicted to find approximately 170 000 galaxy-galaxy strong lenses from its lifetime observation of 14 000 deg^2 of the sky. Detecting this many lenses by visual inspection with professional astronomers and citizen scientists alone is infeasible. Machine learning algorithms, particularly convolutional neural networks (CNNs), have been used as an automated method of detecting strong lenses, and have proven fruitful in finding galaxy-galaxy strong lens candidates. We identify the major challenge to be the automatic detection of galaxy-galaxy strong lenses while simultaneously maintaining a low false positive rate. One aim of this research is to have a quantified starting point on the achieved purity and completeness with our current version of CNN-based detection pipelines for the VIS images of EWS. We select all sources with VIS IE < 23 mag from the Euclid Early Release Observation imaging of the Perseus field. We apply a range of CNN architectures to detect strong lenses in these cutouts. All our networks perform extremely well on simulated data sets and their respective validation sets. However, when applied to real Euclid imaging, the highest lens purity is just 11%. Among all our networks, the false positives are typically identifiable by human volunteers as, for example, spiral galaxies, multiple sources, and artefacts, implying that improvements are still possible, perhaps via a second, more interpretable lens selection filtering stage. There is currently no alternative to human classification of CNN-selected lens candidates. Given the expected 10^5 lensing systems in Euclid, this implies 10^6 objects for human classification, which while very large is not in principle intractable and not without precedent. △ Less

Submitted 25 November, 2024; originally announced November 2024.

Comments: 22 pages, 11 figures, Euclid consortium paper, A&A submitted

The overconcentrated dark halo in the strong lens SDSS J0946+1006 is a subhalo: evidence for self interacting dark matter?

Authors: Wolfgang J. R. Enzi, Coleman M. Krawczyk, Daniel J. Ballard, Thomas E. Collett

Abstract: The nature of dark matter is poorly constrained on subgalactic scales. Alternative models to cold dark matter, such as warm dark matter or self-interacting dark matter, could produce very different dark haloes on these scales. One of the few known dark haloes smaller than a galaxy was discovered in the triple source plane strong lens system J0946+1006. Previous studies have found that this structu… ▽ More The nature of dark matter is poorly constrained on subgalactic scales. Alternative models to cold dark matter, such as warm dark matter or self-interacting dark matter, could produce very different dark haloes on these scales. One of the few known dark haloes smaller than a galaxy was discovered in the triple source plane strong lens system J0946+1006. Previous studies have found that this structure is much more concentrated than expected in $Λ$CDM, but have assumed the dark halo is at the same redshift as the main deflector ($z_{\rm main}=0.222$). In this paper, we fit for the redshift of this dark halo. We reconstruct the first two sources in the system using a forward modelling approach, allowing for additional complexity from multipole perturbations. We find that the perturber redshift is $z_{\rm halo} = {0.207}^{+0.019}_{-0.019}$, and lower bounds on the evidence strongly prefer a subhalo over a line-of-sight structure. Whilst modelling both background sources does not improve constraints on the redshift of the subhalo, it breaks important degeneracies affecting the reconstruction of multipole perturbations. We find that the subhalo is a more than $5σ$ outlier from the $Λ$CDM $v_{\rm max}$-$r_{\rm max}$ relation and has a steep profile with an average slope of $γ_{\rm 2D} = {-1.81}^{+0.15}_{-0.11}$ for radii between $0.75-1.25$ kpc. This steep slope might indicate dark matter self-interactions causing the subhalo to undergo gravothermal collapse; such collapsed haloes are expected to have $γ_{\rm 2D} \approx -2$. △ Less

Submitted 13 November, 2024; originally announced November 2024.

Comments: 16 pages, 10 figures, 2 tables

Correcting for Selection Biases in the Determination of the Hubble Constant from Time-Delay Cosmography

Authors: Tian Li, Thomas E. Collett, Philip J. Marshall, Sydney Erickson, Wolfgang Enzi, Lindsay Oldham, Daniel Ballard

Abstract: The time delay between multiple images of strongly lensed quasars has been used to infer the Hubble constant. The primary systematic uncertainty for time-delay cosmography is the mass-sheet transform (MST), which preserves the lensing observables while altering the inferred $H_0$. The TDCOSMO collaboration used velocity dispersion measurements of lensed quasars and lensed galaxies to infer that ma… ▽ More The time delay between multiple images of strongly lensed quasars has been used to infer the Hubble constant. The primary systematic uncertainty for time-delay cosmography is the mass-sheet transform (MST), which preserves the lensing observables while altering the inferred $H_0$. The TDCOSMO collaboration used velocity dispersion measurements of lensed quasars and lensed galaxies to infer that mass sheets are present, which decrease the inferred $H_0$ by 8$\%$. Here, we test the assumption that the density profiles of galaxy-galaxy and galaxy-quasar lenses are the same. We use a composite star-plus-dark-matter mass profile for the parent deflector population and model the selection function for galaxy-galaxy and galaxy-quasar lenses. We find that a power-law density profile with an MST is a good approximation to a two-component mass profile around the Einstein radius, but we find that galaxy-galaxy lenses have systematically higher mass-sheet components than galaxy-quasar lenses. For individual systems, $λ_\mathrm{int}$ correlates with the ratio of the half-light radius and Einstein radius of the lens. By propagating these results through the TDCOSMO methodology, we find that $H_0$ is lowered by a further $\sim$3\%. Using the velocity dispersions from \citet{slacs9} and our fiducial model for selection biases, we infer $H_0 = 66\pm4 \ \mathrm{(stat)} \pm 1 \ \mathrm{(model \ sys)} \pm 2 \ \mathrm{(measurement \ sys)} \ \mathrm{km} \ \mathrm{s}^{-1} \ \mathrm{Mpc}^{-1}$ for the TDCOSMO plus SLACS dataset. The first residual systematic error is due to plausible alternative choices in modeling the selection function, and the second is an estimate of the remaining systematic error in the measurement of velocity dispersions for SLACS lenses. Accurate time-delay cosmography requires precise velocity dispersion measurements and accurate calibration of selection biases. △ Less

Submitted 19 March, 2025; v1 submitted 21 October, 2024; originally announced October 2024.

Euclid: The Early Release Observations Lens Search Experiment

Authors: J. A. Acevedo Barroso, C. M. O'Riordan, B. Clément, C. Tortora, T. E. Collett, F. Courbin, R. Gavazzi, R. B. Metcalf, V. Busillo, I. T. Andika, R. Cabanac, H. M. Courtois, J. Crook-Mansour, L. Delchambre, G. Despali, L. R. Ecker, A. Franco, P. Holloway, N. Jackson, K. Jahnke, G. Mahler, L. Marchetti, P. Matavulj, A. Melo, M. Meneghetti , et al. (184 additional authors not shown)

Abstract: 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 $0.7\,\rm{deg}^2$ Euclid Early Release Observations data towards the Perseus cluster using both the high-resolution $I_{\scriptscriptstyle\rm E}$ band and the lower-resolution $Y_{\scriptscriptstyle\rm E}$, $J_{\scriptscriptstyle\rm E}$,… ▽ More 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 $0.7\,\rm{deg}^2$ Euclid Early Release Observations data towards the Perseus cluster using both the high-resolution $I_{\scriptscriptstyle\rm E}$ band and the lower-resolution $Y_{\scriptscriptstyle\rm E}$, $J_{\scriptscriptstyle\rm E}$, $H_{\scriptscriptstyle\rm E}$ bands. Each extended source brighter than magnitude 23 in $I_{\scriptscriptstyle\rm E}$ was inspected by 41 expert human classifiers. This amounts to $12\,086$ stamps of $10^{\prime\prime}\,\times\,10^{\prime\prime}$. We found $3$ grade A and $13$ grade B candidates. We assessed the validity of these $16$ candidates by modelling them and checking that they are consistent with a single source lensed by a plausible mass distribution. Five of the candidates pass this check, five others are rejected by the modelling, and six are inconclusive. Extrapolating from the five successfully modelled candidates, we infer that the full $14\,000\,{\rm deg}^2$ of the Euclid Wide Survey should contain $100\,000^{+70\,000}_{-30\,000}$ galaxy-galaxy lenses that are both discoverable through visual inspection and have valid lens models. This is consistent with theoretical forecasts of $170\,000$ discoverable galaxy-galaxy lenses in Euclid. Our five modelled lenses have Einstein radii in the range $0.\!\!^{\prime\prime}68\,<\,θ_\mathrm{E}\,<1.\!\!^{\prime\prime}24$, but their Einstein radius distribution is on the higher side when compared to theoretical forecasts. This suggests that our methodology is likely missing small-Einstein-radius systems. Whilst it is implausible to visually inspect the full Euclid dataset, our results corroborate the promise that Euclid will ultimately deliver a sample of around $10^5$ galaxy-scale lenses. △ Less

Submitted 2 May, 2025; v1 submitted 12 August, 2024; originally announced August 2024.

Comments: Replacement after peer review. 16 pages, 17 figures, Zenodo appendix at https://zenodo.org/records/14946028

Journal ref: A&A 697, A14 (2025)

Find the haystacks, then look for needles: The rate of strongly lensed transients in galaxy-galaxy strong gravitational lenses

Authors: Ana Sainz de Murieta, Thomas E. Collett, Mark R. Magee, Justin D. R. Pierel, Wolfgang J. R. Enzi, Martine Lokken, Alex Gagliano, Dan Ryczanowski

Abstract: The time delay between appearances of multiple images of a gravitationally lensed supernova (glSN) is sensitive to the Hubble constant, $H_0$. As well as time delays, a lensed host galaxy is needed to enable precise inference of $H_0$. In this work we investigate the connection between discoverable lensed transients and their host galaxies. We find that LSST will discover 88 glSNe per year, of whi… ▽ More The time delay between appearances of multiple images of a gravitationally lensed supernova (glSN) is sensitive to the Hubble constant, $H_0$. As well as time delays, a lensed host galaxy is needed to enable precise inference of $H_0$. In this work we investigate the connection between discoverable lensed transients and their host galaxies. We find that LSST will discover 88 glSNe per year, of which $54\%$ will also have a strongly lensed host. The rates can change by approximately 30 percent uncertainty depending primarily on the choice of unlensed SN population and uncertainties in the redshift evolution of the deflector population, but the fraction of glSNe with a lensed host is consistently around a half. LSST will discover 20 glSNe per year in systems that could plausibly have been identified by Euclid as galaxy-galaxy lenses before the discovery of the glSN. Such systems have preferentially longer time delays and therefore are well suited for cosmography. We define a golden sample of glSNe Ia with time delays over 10 days, image separations greater than 0.8 arcseconds, and a multiply imaged host. For this golden sample, we find $91\%$ occur in systems that should already be discoverable as galaxy-galaxy lenses in Euclid. For cosmology with glSNe, monitoring Euclid lenses is a plausible alternative to searching the entire LSST alert stream. △ Less

Submitted 4 July, 2024; originally announced July 2024.

Comments: 14 pages, 11 figures. Submitted to MNRAS

Strong gravitational lenses from the Vera C. Rubin Observatory

Authors: Anowar J. Shajib, Graham P. Smith, Simon Birrer, Aprajita Verma, Nikki Arendse, Thomas E. Collett, Tansu Daylan, Stephen Serjeant, the LSST Strong Lensing Science Collaboration

Abstract: Like many areas of astrophysics and cosmology, the Vera C. Rubin Observatory will be transformational for almost all the applications of strong lensing, thanks to the dramatic increase in the number of known strong lenses by two orders of magnitude or more and the readily available time-domain data for the lenses with transient sources. In this article, we provide an overview of the forecasted num… ▽ More Like many areas of astrophysics and cosmology, the Vera C. Rubin Observatory will be transformational for almost all the applications of strong lensing, thanks to the dramatic increase in the number of known strong lenses by two orders of magnitude or more and the readily available time-domain data for the lenses with transient sources. In this article, we provide an overview of the forecasted number of discovered lenses of different types and describe the primary science cases these large lens samples will enable. We provide an updated forecast on the joint constraint for the dark energy equation-of-state parameters, $w_0$ and $w_a$, from combining all strong lensing probes of dark energy. We update the previous forecast from the Rubin Observatory Dark Energy Science Collaboration's Science Review Document by adding two new crucial strong lensing samples: lensed Type Ia supernovae and single-deflector lenses with measured stellar kinematics. Finally, we describe the current and near-future activities and collaborative efforts within the strong lensing community in preparation for the arrival of the first real dataset from Rubin in early 2026. △ Less

Submitted 17 February, 2025; v1 submitted 13 June, 2024; originally announced June 2024.

Comments: 13 pages, 2 figures. Invited review for the Royal Society meeting "Multi-messenger Gravitational Lensing", accepted by Philosophical Transactions A

Euclid. I. Overview of the Euclid mission

Authors: Euclid Collaboration, Y. Mellier, Abdurro'uf, J. A. Acevedo Barroso, A. Achúcarro, J. Adamek, R. Adam, G. E. Addison, N. Aghanim, M. Aguena, V. Ajani, Y. Akrami, A. Al-Bahlawan, A. Alavi, I. S. Albuquerque, G. Alestas, G. Alguero, A. Allaoui, S. W. Allen, V. Allevato, A. V. Alonso-Tetilla, B. Altieri, A. Alvarez-Candal, S. Alvi, A. Amara , et al. (1115 additional authors not shown)

Abstract: The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14… ▽ More The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance. △ Less

Submitted 24 September, 2024; v1 submitted 22 May, 2024; originally announced May 2024.

Comments: Accepted for publication in the A&A special issue`Euclid on Sky'

Journal ref: A&A 697, A1 (2025)

Lensed Type Ia Supernova "Encore" at z=2: The First Instance of Two Multiply-Imaged Supernovae in the Same Host Galaxy

Authors: J. D. R. Pierel, A. B. Newman, S. Dhawan, M. Gu, B. A. Joshi, T. Li, S. Schuldt, L. G. Strolger, S. H. Suyu, G. B. Caminha, S. H. Cohen, J. M. Diego, J. C. J. Dsilva, S. Ertl, B. L. Frye, G. Granata, C. Grillo, A. M. Koekemoer, J. Li, A. Robotham, J. Summers, T. Treu, R. A. Windhorst, A. Zitrin, S. Agarwal , et al. (38 additional authors not shown)

Abstract: A bright ($m_{\rm F150W,AB}$=24 mag), $z=1.95$ supernova (SN) candidate was discovered in JWST/NIRCam imaging acquired on 2023 November 17. The SN is quintuply-imaged as a result of strong gravitational lensing by a foreground galaxy cluster, detected in three locations, and remarkably is the second lensed SN found in the same host galaxy. The previous lensed SN was called "Requiem", and therefore… ▽ More A bright ($m_{\rm F150W,AB}$=24 mag), $z=1.95$ supernova (SN) candidate was discovered in JWST/NIRCam imaging acquired on 2023 November 17. The SN is quintuply-imaged as a result of strong gravitational lensing by a foreground galaxy cluster, detected in three locations, and remarkably is the second lensed SN found in the same host galaxy. The previous lensed SN was called "Requiem", and therefore the new SN is named "Encore". This makes the MACS J0138.0$-$2155 cluster the first known system to produce more than one multiply-imaged SN. Moreover, both SN Requiem and SN Encore are Type Ia SNe (SNe Ia), making this the most distant case of a galaxy hosting two SNe Ia. Using parametric host fitting, we determine the probability of detecting two SNe Ia in this host galaxy over a $\sim10$ year window to be $\approx3\%$. These observations have the potential to yield a Hubble Constant ($H_0$) measurement with $\sim10\%$ precision, only the third lensed SN capable of such a result, using the three visible images of the SN. Both SN Requiem and SN Encore have a fourth image that is expected to appear within a few years of $\sim2030$, providing an unprecedented baseline for time-delay cosmography. △ Less

Submitted 22 July, 2024; v1 submitted 2 April, 2024; originally announced April 2024.

Comments: Accepted, ApJL

Two-dimensional kinematics and dynamical modelling of the 'Jackpot' gravitational lens from deep MUSE observations

Authors: Hannah C. Turner, Russell J. Smith, Thomas E. Collett

Abstract: We present results from the first spatially resolved kinematic and dynamical modelling analysis of the unique SDSSJ0946+1006 ('Jackpot') triple-source lens system, where a single massive foreground $z\,=\,0.222$ galaxy multiple-images three background sources at different redshifts. Deep IFU spectroscopic data were obtained using the MUSE instrument on the VLT, which, compared to previous single-s… ▽ More We present results from the first spatially resolved kinematic and dynamical modelling analysis of the unique SDSSJ0946+1006 ('Jackpot') triple-source lens system, where a single massive foreground $z\,=\,0.222$ galaxy multiple-images three background sources at different redshifts. Deep IFU spectroscopic data were obtained using the MUSE instrument on the VLT, which, compared to previous single-slit observations, provides full azimuthal area coverage, high sensitivity (5 hour integration) and high angular resolution ($0.5\,$arcsec FWHM). To account for the strong continuum contributions from the $z\,=\,0.609$ source, a multiple-component stellar template fitting technique is adopted to fit to the spectra of both the lens galaxy and the bright lensed background arc simultaneously. Through this, we robustly measure the first and second moments of the two-dimensional stellar kinematics out to about $10\,$kpc from the centre of the lens, as well as resolving the inner profile inwards to $\sim1\,$kpc. The two-dimensional kinematic maps show a steep velocity dispersion gradient and a clear rotational component. We constrain the characteristic properties of the stellar and dark matter (DM) mass components with a sufficiently flexible parameterised dynamical model and an imposed lensing mass and find a DM density slope of $γ\,=\,1.73\substack{+0.17 \\ -0.26}$, i.e. significantly steeper than an unmodified NFW profile ($γ\,=\,1$) and consistent with a contracted DM halo. Our fitted models have a lensing-equivalent density slope of $η\,=\,0.96\pm0.02$, and thus we confirm most pure lensing results in finding a near isothermal profile for this galaxy. △ Less

Submitted 16 January, 2024; originally announced January 2024.

Comments: 17 pages, 16 figures. Version accepted by MNRAS

Gravitational imaging through a triple source plane lens: revisiting the $Λ$CDM-defying dark subhalo in SDSSJ0946+1006

Authors: Daniel J. Ballard, Wolfgang J. R. Enzi, Thomas E. Collett, Hannah C. Turner, Russell J. Smith

Abstract: The $Λ$CDM paradigm successfully explains the large-scale structure of the Universe, but is less well constrained on sub-galactic scales. Gravitational lens modelling has been used to measure the imprints of dark substructures on lensed arcs, testing the small-scale predictions of $Λ$CDM. However, the methods required for these tests are subject to degeneracies among the lens mass model and the so… ▽ More The $Λ$CDM paradigm successfully explains the large-scale structure of the Universe, but is less well constrained on sub-galactic scales. Gravitational lens modelling has been used to measure the imprints of dark substructures on lensed arcs, testing the small-scale predictions of $Λ$CDM. However, the methods required for these tests are subject to degeneracies among the lens mass model and the source light profile. We present a case study of the unique compound gravitational lens SDSSJ0946+1006, wherein a dark, massive substructure has been detected, whose reported high concentration would be unlikely in a $Λ$CDM universe. For the first time, we model the first two background sources in both I- and U-band HST imaging, as well as VLT-MUSE emission line data for the most distant source. We recover a lensing perturber at a $5.9σ$ confidence level with mass $\log_{10}(M_\mathrm{sub}/M_{\odot})=9.2^{+0.4}_{-0.1}$ and concentration $\log_{10}c=2.4^{+0.5}_{-0.3}$. The concentration is more consistent with CDM subhalos than previously reported, and the mass is compatible with that of a dwarf satellite galaxy whose flux is undetectable in the data at the location of the perturber. A wandering black hole with mass $\log_{10}(M_\mathrm{BH}/M_{\odot})=8.9^{+0.2}_{-0.1}$ is a viable alternative model. We systematically investigate alternative assumptions about the complexity of the mass distribution and source reconstruction; in all cases the subhalo is detected at around the $\geq5σ$ level. However, the detection significance can be altered substantially (up to $11.3σ$) by alternative choices for the source regularisation scheme. △ Less

Submitted 28 February, 2024; v1 submitted 8 September, 2023; originally announced September 2023.

Comments: 24 pages, 16 figures, 5 appendices

Journal ref: Monthly Notices of the Royal Astronomical Society, Volume 528, Issue 4, March 2024, Pages 7564-7586

Lensed type Ia supernovae in light of SN Zwicky and iPTF16geu

Authors: Ana Sainz de Murieta, Thomas E. Collett, Mark R. Magee, Luke Weisenbach, Coleman M. Krawczyk, Wolfgang Enzi

Abstract: Strong gravitationally lensed supernovae (glSNe) are a powerful probe to obtain a measure of the expansion rate of the Universe, but they are also extremely rare. To date, only two glSNe with multiple images strongly lensed by galaxies have been found, but their short time delays make them unsuitable for cosmography. Here, we simulate a realistic catalogue of lensed supernovae and study the charac… ▽ More Strong gravitationally lensed supernovae (glSNe) are a powerful probe to obtain a measure of the expansion rate of the Universe, but they are also extremely rare. To date, only two glSNe with multiple images strongly lensed by galaxies have been found, but their short time delays make them unsuitable for cosmography. Here, we simulate a realistic catalogue of lensed supernovae and study the characteristics of the population of detectable systems for different surveys. Compared to previous studies, our simulations also account for the effect of microlensing and its impact on the glSNe yields. We show that the properties of glSNe in shallow surveys (such as the Zwicky Transient Facility; ZTF) are determined by the need for large magnifications, which favours systems of four images with short time delays and low image separations. This picture is consistent with the properties of iPTF16geu and SN Zwicky, but is not representative of the population found in deeper surveys, which are limited by the volume of the Universe that is strongly lensed. For deeper surveys, such as the Legacy Survey of Space and Time (LSST), glSNe show longer time delays and greater angular separations, and the inclusion of microlensing results in 8$\%$ of glSNe becoming demagnified under the detection threshold. In the 10 years of the survey LSST should be able to find $\approx$ 180 systems, of which 70 will be suited for cosmography enabling a $\approx$ 1.2$\%$ precision $H_0$ measurement with LSST glSNe. △ Less

Submitted 4 October, 2023; v1 submitted 24 July, 2023; originally announced July 2023.

Comments: 12 pages, 9 figures. Submitted

Cosmology from Large Populations of Galaxy-Galaxy Strong Gravitational Lenses

Authors: Tian Li, Thomas E. Collett, Coleman M. Krawczyk, Wolfgang Enzi

Abstract: We present a forecast analysis on the feasibility of measuring the cosmological parameters with a large number of galaxy-galaxy scale strong gravitational lensing systems. Future wide area surveys are expected to discover and measure the properties of more than 10 000 strong lensing systems. We develop a hierarchical model that can simultaneously constrain the lens population and cosmological para… ▽ More We present a forecast analysis on the feasibility of measuring the cosmological parameters with a large number of galaxy-galaxy scale strong gravitational lensing systems. Future wide area surveys are expected to discover and measure the properties of more than 10 000 strong lensing systems. We develop a hierarchical model that can simultaneously constrain the lens population and cosmological parameters by combining Einstein radius measurements with stellar dynamical mass estimates for every lens. Marginalizing over the lens density profiles and stellar orbital anisotropies, we find that $w$ can be constrained to a precision of $0.11$ with 10 000 galaxy-galaxy lens systems, which would be better than any existing single-probe constraint. We test our method on 161 existing lenses, finding $w=-0.96\pm0.46$. We also show how to mitigate against the potential systematic of redshift evolution in the mean lens density profile of the population. △ Less

Submitted 18 July, 2023; originally announced July 2023.

A search for gravitationally lensed supernovae within the Zwicky Transient Facility public survey

Authors: M. R. Magee, A. Sainz de Murieta, T. E. Collett, W. Enzi

Abstract: Strong gravitational lensing of supernovae is exceedingly rare. To date, only a handful of lensed supernovae are known. Despite this, lensed supernovae have emerged as a promising method for measuring the current expansion rate of the Universe and breaking the Hubble tension. We present an extensive search for gravitationally lensed supernovae within the Zwicky Transient Facility (ZTF) public surv… ▽ More Strong gravitational lensing of supernovae is exceedingly rare. To date, only a handful of lensed supernovae are known. Despite this, lensed supernovae have emerged as a promising method for measuring the current expansion rate of the Universe and breaking the Hubble tension. We present an extensive search for gravitationally lensed supernovae within the Zwicky Transient Facility (ZTF) public survey, covering 15,215 transients with good light curves discovered during four years of observations. We crossmatch a catalogue of known and candidate lens galaxies with our sample and find three coincident sources, which were due to chance alignment. To search for supernovae magnified by unknown lenses, we test multiple methods suggested in the literature for the first time on real data. This includes selecting objects with extremely red colours, those that appear inconsistent with the host galaxy redshift, and those with bright absolute magnitudes inferred from the host galaxy redshift. We find a few hundred candidates, most of which are due to contamination from activate galactic nuclei, bogus detections, or unlensed supernovae. The false positive rate from these methods presents significant challenges for future surveys. In total, 132 unique transients were identified across all of our selection methods that required detailed manual rejection, which would be infeasible for larger samples. Overall, we do not find any compelling candidates for lensed supernovae, which is broadly consistent with previous estimates for the rate of lensed supernovae from the ZTF public survey alone and the number expected to pass the selection cuts we apply. △ Less

Submitted 31 May, 2023; v1 submitted 27 March, 2023; originally announced March 2023.

Comments: Updated selection criteria. 20 pages, 13 figures, and 3 tables including the appendices

The impact of human expert visual inspection on the discovery of strong gravitational lenses

Authors: Karina Rojas, Thomas E. Collett, Daniel Ballard, Mark R. Magee, Simon Birrer, Elizabeth Buckley-Geer., James H. H. Chan, Benjamin Clément, José M. Diego, Fabrizio Gentile, Jimena González, Rémy Joseph, Jorge Mastache, Stefan Schuldt, Crescenzo Tortora, Tomás Verdugo, Aprajita Verma, Tansu Daylan, Martin Millon, Neal Jackson, Simon Dye, Alejandra Melo, Guillaume Mahler, Ricardo L. C. Ogando, Frédéric Courbin , et al. (31 additional authors not shown)

Abstract: We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, an… ▽ More We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with $g$-band signal-to-noise less than $\sim$25 or Einstein radii less than $\sim$1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifier's experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies. △ Less

Submitted 25 April, 2023; v1 submitted 9 January, 2023; originally announced January 2023.

Comments: 16 pages, 20 Figures

Testing Cosmology with Double Source Lensing

Authors: Divij Sharma, Thomas E. Collett, Eric V. Linder

Abstract: Double source lensing provides a dimensionless ratio of distance ratios, a "remote viewing" of cosmology through distances relative to the gravitational lens, beyond the observer. We use this to test the cosmological framework, particularly with respect to spatial curvature and the distance duality relation. We derive a consistency equation for constant spatial curvature, allowing not only the inv… ▽ More Double source lensing provides a dimensionless ratio of distance ratios, a "remote viewing" of cosmology through distances relative to the gravitational lens, beyond the observer. We use this to test the cosmological framework, particularly with respect to spatial curvature and the distance duality relation. We derive a consistency equation for constant spatial curvature, allowing not only the investigation of flat vs curved but of the Friedmann-Lemaître-Robertson-Walker framework itself. For distance duality, we demonstrate that the evolution of the lens mass profile slope must be controlled to $\gtrsim5$ times tighter fractional precision than a claimed distance duality violation. Using LENSPOP forecasts of double source lensing systems in Euclid and LSST surveys we also explore constraints on dark energy equation of state parameters and any evolution of the lens mass profile slope. △ Less

Submitted 20 March, 2023; v1 submitted 30 November, 2022; originally announced December 2022.

Comments: 10 pages, 7 figures. v2 matches version accepted to JCAP

Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky

Authors: Ariel Goobar, Joel Johansson, Steve Schulze, Nikki Arendse, Ana Sagués Carracedo, Suhail Dhawan, Edvard Mörtsell, Christoffer Fremling, Lin Yan, Daniel Perley, Jesper Sollerman, Rémy Joseph, K-Ryan Hinds, William Meynardie, Igor Andreoni, Eric Bellm, Josh Bloom, Thomas E. Collett, Andrew Drake, Matthew Graham, Mansi Kasliwal, Shri Kulkarni, Cameron Lemon, Adam A. Miller, James D. Neill , et al. (13 additional authors not shown)

Abstract: Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. High-cadence optical observations with the Zwicky Transient Facility, w… ▽ More Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. High-cadence optical observations with the Zwicky Transient Facility, with an unparalleled large field of view, led to the detection of a multiply-imaged Type Ia supernova (SN Ia), ``SN Zwicky", a.k.a. SN 2022qmx. Magnified nearly twenty-five times, the system was found thanks to the ``standard candle" nature of SNe Ia. High-spatial resolution imaging with the Keck telescope resolved four images of the supernova with very small angular separation, corresponding to an Einstein radius of only $θ_E =0.167"$ and almost identical arrival times. The small $θ_E$ and faintness of the lensing galaxy is very unusual, highlighting the importance of supernovae to fully characterise the properties of galaxy-scale gravitational lenses, including the impact of galaxy substructures. △ Less

Submitted 14 June, 2023; v1 submitted 1 November, 2022; originally announced November 2022.

Comments: Matches published version in Nature Astronomy

Strong Lensing by Galaxies

Authors: A. J. Shajib, G. Vernardos, T. E. Collett, V. Motta, D. Sluse, L. L. R. Williams, P. Saha, S. Birrer, C. Spiniello, T. Treu

Abstract: Strong gravitational lensing at the galaxy scale is a valuable tool for various applications in astrophysics and cosmology. The primary uses of galaxy-scale lensing are to study elliptical galaxies' mass structure and evolution, constrain the stellar initial mass function, and measure cosmological parameters. Since the discovery of the first galaxy-scale lens in the 1980s, this field has made sign… ▽ More Strong gravitational lensing at the galaxy scale is a valuable tool for various applications in astrophysics and cosmology. The primary uses of galaxy-scale lensing are to study elliptical galaxies' mass structure and evolution, constrain the stellar initial mass function, and measure cosmological parameters. Since the discovery of the first galaxy-scale lens in the 1980s, this field has made significant advancements in data quality and modeling techniques. In this review, we describe the most common methods for modeling lensing observables, especially imaging data, as they are the most accessible and informative source of lensing observables. We then summarize the primary findings from the literature on the astrophysical and cosmological applications of galaxy-scale lenses. We also discuss the current limitations of the data and methodologies and provide an outlook on the expected improvements in both areas in the near future. △ Less

Submitted 6 April, 2025; v1 submitted 19 October, 2022; originally announced October 2022.

Comments: Published in Space Science Reviews, Topical Collection "Strong Gravitational Lensing", eds. J. Wambsganss et al. This version: accepted version

Journal ref: Space Sci Rev 220, 87 (2024)

The AGEL Survey: Spectroscopic Confirmation of Strong Gravitational Lenses in the DES and DECaLS Fields Selected Using Convolutional Neural Networks

Authors: Kim-Vy H. Tran, Anishya Harshan, Karl Glazebrook, G. C. Keerthi Vasan, Tucker Jones, Colin Jacobs, Glenn G. Kacprzak, Tania M. Barone, Thomas E. Collett, Anshu Gupta, Astrid Henderson, Lisa J. Kewley, Sebastian Lopez, Themiya Nanayakkara, Ryan L. Sanders, Sarah M. Sweet

Abstract: We present spectroscopic confirmation of candidate strong gravitational lenses using the Keck Observatory and Very Large Telescope as part of our ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey. We confirm that 1) search methods using Convolutional Neural Networks (CNN) with visual inspection successfully identify strong gravitational lenses and 2) the lenses are at higher redshifts relative t… ▽ More We present spectroscopic confirmation of candidate strong gravitational lenses using the Keck Observatory and Very Large Telescope as part of our ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey. We confirm that 1) search methods using Convolutional Neural Networks (CNN) with visual inspection successfully identify strong gravitational lenses and 2) the lenses are at higher redshifts relative to existing surveys due to the combination of deeper and higher resolution imaging from DECam and spectroscopy spanning optical to near-infrared wavelengths. We measure 104 redshifts in 77 systems selected from a catalog in the DES and DECaLS imaging fields (r<22 mag). Combining our results with published redshifts, we present redshifts for 68 lenses and establish that CNN-based searches are highly effective for use in future imaging surveys with a success rate of 88% (defined as 68/77). We report 53 strong lenses with spectroscopic redshifts for both the deflector and source (z_src>z_defl), and 15 lenses with a spectroscopic redshift for either the deflector (z_defl>0.21) or source (z_src>1.34). For the 68 lenses, the deflectors and sources have average redshifts and standard deviations of 0.58+/-0.14 and 1.92+/-0.59 respectively, and corresponding redshift ranges of (0.21<z_defl<0.89) and (0.88<z_src<3.55). The AGEL systems include 41 deflectors at zdefl>0.5 that are ideal for follow-up studies to track how mass density profiles evolve with redshift. Our goal with AGEL is to spectroscopically confirm ~100 strong gravitational lenses that can be observed from both hemispheres throughout the year. The AGEL survey is a resource for refining automated all-sky searches and addressing a range of questions in astrophysics and cosmology. △ Less

Submitted 26 September, 2022; v1 submitted 11 May, 2022; originally announced May 2022.

Comments: Updated final version of manuscript published by the Astronomical Journal

Snowmass2021 Cosmic Frontier White Paper: Enabling Flagship Dark Energy Experiments to Reach their Full Potential

Authors: Jonathan A. Blazek, Doug Clowe, Thomas E. Collett, Ian P. Dell'Antonio, Mark Dickinson, Lluís Galbany, Eric Gawiser, Katrin Heitmann, Renée Hložek, Mustapha Ishak, Saurabh W. Jha, Alex G. Kim, C. Danielle Leonard, Anja von der Linden, Michelle Lochner, Rachel Mandelbaum, Peter Melchior, Joel Meyers, Jeffrey A. Newman, Peter Nugent, Saul Perlmutter, Daniel J. Perrefort, Javier Sánchez, Samuel J. Schmidt, Sukhdeep Singh , et al. (3 additional authors not shown)

Abstract: A new generation of powerful dark energy experiments will open new vistas for cosmology in the next decade. However, these projects cannot reach their utmost potential without data from other telescopes. This white paper focuses in particular on the compelling benefits of ground-based spectroscopic and photometric observations to complement the Vera C. Rubin Observatory, as well as smaller program… ▽ More A new generation of powerful dark energy experiments will open new vistas for cosmology in the next decade. However, these projects cannot reach their utmost potential without data from other telescopes. This white paper focuses in particular on the compelling benefits of ground-based spectroscopic and photometric observations to complement the Vera C. Rubin Observatory, as well as smaller programs in aid of a DESI-2 experiment and CMB-S4. These additional data sets will both improve dark energy constraints from these flagship projects beyond what would possible on their own and open completely new windows into fundamental physics. For example, additional photometry and single-object spectroscopy will provide necessary follow-up information for supernova and strong lensing cosmology, while highly-multiplexed spectroscopy both from smaller facilities over wide fields and from larger facilities over narrower regions of sky will yield more accurate photometric redshift estimates for weak lensing and galaxy clustering measurements from the Rubin Observatory, provide critical spectroscopic host galaxy redshifts for supernova Hubble diagrams, provide improved understanding of limiting astrophysical systematic effects, and enable new measurements that probe the nature of gravity. A common thread is that access to complementary data from a range of telescopes/instruments would have a substantial impact on the rate of advance of dark energy science in the coming years. △ Less

Submitted 5 April, 2022; originally announced April 2022.

Comments: White paper submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)

LensingETC: a tool to optimize multi-filter imaging campaigns of galaxy-scale strong lensing systems

Authors: Anowar J. Shajib, Karl Glazebrook, Tania Barone, Geraint F. Lewis, Tucker Jones, Kim-Vy H. Tran, Elizabeth Buckley-Geer, Thomas E. Collett, Joshua Frieman, Colin Jacobs

Abstract: Imaging data is the principal observable required to use galaxy-scale strong lensing in a multitude of applications in extragalactic astrophysics and cosmology. In this paper, we develop Lensing Exposure Time Calculator (LensingETC) to optimize the efficiency of telescope time usage when planning multi-filter imaging campaigns for galaxy-scale strong lenses. This tool simulates realistic data tail… ▽ More Imaging data is the principal observable required to use galaxy-scale strong lensing in a multitude of applications in extragalactic astrophysics and cosmology. In this paper, we develop Lensing Exposure Time Calculator (LensingETC) to optimize the efficiency of telescope time usage when planning multi-filter imaging campaigns for galaxy-scale strong lenses. This tool simulates realistic data tailored to specified instrument characteristics and then automatically models them to assess the power of the data in constraining lens model parameters. We demonstrate a use case of this tool by optimizing a two-filter observing strategy (in IR and UVIS) within the limited exposure time per system allowed by a Hubble Space Telescope (HST) Snapshot program. We find that higher resolution is more advantageous to gain constraining power on the lensing observables, when there is a trade-off between signal-to-noise ratio and resolution; e.g., between the UVIS and IR filters of the HST. We also find that, whereas a point spread function (PSF) with sub-Nyquist sampling allows the sample mean for a model parameter to be robustly recovered for both galaxy-galaxy and point-source lensing systems, a sub-Nyquist sampled PSF introduces a larger scatter than a Nyquist sampled one in the deviation from the ground truth for point-source lens systems. △ Less

Submitted 10 March, 2022; originally announced March 2022.

Comments: 10 pages, 7 figures, 3 tables

A fully-spectroscopic triple-source-plane lens: the Jackpot completed

Authors: Russell J. Smith, Thomas E. Collett

Abstract: We present a spectroscopic determination of the redshift of the second source in the Jackpot gravitational lens system J0946+1006, for which only a photometric estimate of $z_{\rm phot}$ = 2.41$^{+0.04}_{-0.21}$ has previously been available. By visually inspecting an archival VLT X-Shooter observation, we located a single emission line from the source in the H-band. Among the possible options we… ▽ More We present a spectroscopic determination of the redshift of the second source in the Jackpot gravitational lens system J0946+1006, for which only a photometric estimate of $z_{\rm phot}$ = 2.41$^{+0.04}_{-0.21}$ has previously been available. By visually inspecting an archival VLT X-Shooter observation, we located a single emission line from the source in the H-band. Among the possible options we find that this line is most likely to be [OIII] 5007 Ang at $z_{\rm spec} $ = 2.035. Guided by this proposal, we were able to detect the faint CIII] 1907,1909 Ang emission doublet in a deep VLT MUSE datacube. The CIII] emission is spatially coincident with the brightest parts of the second Einstein ring, and strongly supports the redshift identification. The spectroscopic redshift is only marginally consistent with the photometric estimate. Re-examining the cosmological constraints from J0946+1006, the revised measurement favours less negative values of the dark energy equation-of-state parameter $w$; when combined with a cosmic microwave background prior, we infer $w$ = $-1.04\pm0.20$. The revised redshift does not significantly help to reconcile the small discrepancy in the image positions for the even more distant third source in J0946+1006. △ Less

Submitted 26 April, 2021; originally announced April 2021.

Comments: To be resubmitted to MNRAS following very minor comments from referee

Localizing merging black holes with sub-arcsecond precision using gravitational-wave lensing

Authors: Otto A. Hannuksela, Thomas E. Collett, Mesut Çalışkan, Tjonnie G. F. Li

Abstract: The current gravitational-wave localization methods rely mainly on sources with electromagnetic counterparts. Unfortunately, a binary black hole does not emit light. Due to this, it is generally not possible to localize these objects precisely. However, strongly lensed gravitational waves, which are forecasted in this decade, could allow us to localize the binary by locating its lensed host galaxy… ▽ More The current gravitational-wave localization methods rely mainly on sources with electromagnetic counterparts. Unfortunately, a binary black hole does not emit light. Due to this, it is generally not possible to localize these objects precisely. However, strongly lensed gravitational waves, which are forecasted in this decade, could allow us to localize the binary by locating its lensed host galaxy. Identifying the correct host galaxy is challenging because there are hundreds to thousands of other lensed galaxies within the sky area spanned by the gravitational-wave observation. However, we can constrain the lensing galaxy's physical properties through both gravitational-wave and electromagnetic observations. We show that these simultaneous constraints allow one to localize quadruply lensed waves to one or at most a few galaxies with the LIGO/Virgo/Kagra network in typical scenarios. Once we identify the host, we can localize the binary to two sub-arcsec regions within the host galaxy. Moreover, we demonstrate how to use the system to measure the Hubble constant as a proof-of-principle application. △ Less

Submitted 18 August, 2020; v1 submitted 28 April, 2020; originally announced April 2020.

Comments: 5 pages (main text) + 5 pages (methods+references), 5 figures. Accepted to MNRAS

A Triple Rollover: A third multiply-imaged source at z~6 behind the Jackpot gravitational lens

Authors: Thomas E. Collett, Russell J. Smith

Abstract: UUsing a five-hour adaptive-optics-assisted observation with MUSE, we have identified a doubly-imaged Ly alpha source at redshift 5.975 behind the z=0.222 lens galaxy J0946+1006 ('the Jackpot'). The source separation implies an Einstein radius of ~2.5 arcsec. Combined with the two previously-known Einstein rings in this lens (radii 1.4 arcsec at z = 0.609 and 2.1 arcsec at z ~ 2.4), this system is… ▽ More UUsing a five-hour adaptive-optics-assisted observation with MUSE, we have identified a doubly-imaged Ly alpha source at redshift 5.975 behind the z=0.222 lens galaxy J0946+1006 ('the Jackpot'). The source separation implies an Einstein radius of ~2.5 arcsec. Combined with the two previously-known Einstein rings in this lens (radii 1.4 arcsec at z = 0.609 and 2.1 arcsec at z ~ 2.4), this system is now a unique galaxy-scale triple-source-plane lens. We show that existing lensing models for J0946+1006 successfully map the two new observed images to a common point on the z=5.975 source plane. The new source will provide further constraints on the mass distribution in the lens and in the two previously known sources. The third source also probes two new distance scaling factors which are sensitive to the cosmological parameters of the Universe. We show that detection of a new multiply imaged emission-line source is not unexpected in observations of this depth; similar data for other known lenses should reveal a larger sample of multiple-image-plane systems for cosmography and other applications. △ Less

Submitted 22 June, 2020; v1 submitted 1 April, 2020; originally announced April 2020.

Comments: 7 pages. MNRAS Accepted. The authors contributed equally to this work

Observing the earliest moments of supernovae using strong gravitational lenses

Authors: Max Foxley-Marrable, Thomas E. Collett, Chris Frohmaier, Daniel A. Goldstein, Daniel Kasen, Elizabeth Swann, David Bacon

Abstract: We determine the viability of exploiting lensing time delays to observe strongly gravitationally lensed supernovae (gLSNe) from first light. Assuming a plausible discovery strategy, the Legacy Survey of Space and Time (LSST) and the Zwicky Transient Facility (ZTF) will discover $\sim$ 110 and $\sim$ 1 systems per year before the supernova (SN) explosion in the final image respectively. Systems wil… ▽ More We determine the viability of exploiting lensing time delays to observe strongly gravitationally lensed supernovae (gLSNe) from first light. Assuming a plausible discovery strategy, the Legacy Survey of Space and Time (LSST) and the Zwicky Transient Facility (ZTF) will discover $\sim$ 110 and $\sim$ 1 systems per year before the supernova (SN) explosion in the final image respectively. Systems will be identified $11.7^{+29.8}_{-9.3}$ days before the final explosion. We then explore the possibility of performing early-time observations for Type IIP and Type Ia SNe in LSST-discovered systems. Using a simulated Type IIP explosion, we predict that the shock breakout in one trailing image per year will peak at $\lesssim$ 24.1 mag ($\lesssim$ 23.3) in the $B$-band ($F218W$), however evolving over a timescale of $\sim$ 30 minutes. Using an analytic model of Type Ia companion interaction, we find that in the $B$-band we should observe at least one shock cooling emission event per year that peaks at $\lesssim$ 26.3 mag ($\lesssim$ 29.6) assuming all Type Ia gLSNe have a 1 M$_\odot$ red giant (main sequence) companion. We perform Bayesian analysis to investigate how well deep observations with 1 hour exposures on the European Extremely Large Telescope would discriminate between Type Ia progenitor populations. We find that if all Type Ia SNe evolved from the double-degenerate channel, then observations of the lack of early blue flux in 10 (50) trailing images would rule out more than 27% (19%) of the population having 1 M$_\odot$ main sequence companions at 95% confidence. △ Less

Submitted 8 May, 2020; v1 submitted 31 March, 2020; originally announced March 2020.

Comments: 17 pages, 15 figures (including appendices). Accepted by MNRAS 3rd May 2020

The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2016 follow-up campaign. I. Overview and classification of candidates selected by two techniques

Authors: T. Treu, A. Agnello, M. A. Baumer, S. Birrer, E. J. Buckley-Geer, F. Courbin, Y. J. Kim, H. Lim, P. J. Marshall, B. Nord, P. L. Schechter, P. R. Sivakumar, L. E. Abramson, T. Anguita, Y. Apostolovski, M. W. Auger, J. H. H. Chan, G. C. F. Chen, T. E. Collett, C. D. Fassnacht, J. -W. Hsueh, C. Lemon, R. G. McMahon, V. Motta, F. Ostrovski , et al. (57 additional authors not shown)

Abstract: The primary goals of the STRong lensing Insights into the Dark Energy Survey (STRIDES) collaboration are to measure the dark energy equation of state parameter and the free streaming length of dark matter. To this aim, STRIDES is discovering strongly lensed quasars in the imaging data of the Dark Energy Survey and following them up to measure time delays, high resolution imaging, and spectroscopy… ▽ More The primary goals of the STRong lensing Insights into the Dark Energy Survey (STRIDES) collaboration are to measure the dark energy equation of state parameter and the free streaming length of dark matter. To this aim, STRIDES is discovering strongly lensed quasars in the imaging data of the Dark Energy Survey and following them up to measure time delays, high resolution imaging, and spectroscopy sufficient to construct accurate lens models. In this paper, we first present forecasts for STRIDES. Then, we describe the STRIDES classification scheme, and give an overview of the Fall 2016 follow-up campaign. We continue by detailing the results of two selection methods, the Outlier Selection Technique and a morphological algorithm, and presenting lens models of a system, which could possibly be a lensed quasar in an unusual configuration. We conclude with the summary statistics of the Fall 2016 campaign. Including searches presented in companion papers (Anguita et al.; Ostrovski et al.), STRIDES followed up 117 targets identifying 7 new strongly lensed systems, and 7 nearly identical quasars (NIQs), which could be confirmed as lenses by the detection of the lens galaxy. 76 candidates were rejected and 27 remain otherwise inconclusive, for a success rate in the range 6-35\%. This rate is comparable to that of previous searches like SQLS even though the parent dataset of STRIDES is purely photometric and our selection of candidates cannot rely on spectroscopic information. △ Less

Submitted 5 September, 2018; v1 submitted 14 August, 2018; originally announced August 2018.

Comments: (MNRAS in press; color scheme of Figures 1-4 improved with respect to v1)

Is every strong lens model unhappy in its own way? Uniform modelling of a sample of 13 quadruply+ imaged quasars

Authors: A. J. Shajib, S. Birrer, T. Treu, M. W. Auger, A. Agnello, T. Anguita, E. J. Buckley-Geer, J. H. H. Chan, T. E. Collett, F. Courbin, C. D. Fassnacht, J. Frieman, I. Kayo, C. Lemon, H. Lin, P. J. Marshall, R. McMahon, A. More, N. D. Morgan, V. Motta, M. Oguri, F. Ostrovski, C. E. Rusu, P. L. Schechter, T. Shanks , et al. (48 additional authors not shown)

Abstract: Strong-gravitational lens systems with quadruply-imaged quasars (quads) are unique probes to address several fundamental problems in cosmology and astrophysics. Although they are intrinsically very rare, ongoing and planned wide-field deep-sky surveys are set to discover thousands of such systems in the next decade. It is thus paramount to devise a general framework to model strong-lens systems to… ▽ More Strong-gravitational lens systems with quadruply-imaged quasars (quads) are unique probes to address several fundamental problems in cosmology and astrophysics. Although they are intrinsically very rare, ongoing and planned wide-field deep-sky surveys are set to discover thousands of such systems in the next decade. It is thus paramount to devise a general framework to model strong-lens systems to cope with this large influx without being limited by expert investigator time. We propose such a general modelling framework (implemented with the publicly available software Lenstronomy) and apply it to uniformly model three-band Hubble Space Telescope Wide Field Camera 3 images of 13 quads. This is the largest uniformly modelled sample of quads to date and paves the way for a variety of studies. To illustrate the scientific content of the sample, we investigate the alignment between the mass and light distribution in the deflectors. The position angles of these distributions are well-aligned, except when there is strong external shear. However, we find no correlation between the ellipticity of the light and mass distributions. We also show that the observed flux-ratios between the images depart significantly from the predictions of simple smooth models. The departures are strongest in the bluest band, consistent with microlensing being the dominant cause in addition to millilensing. Future papers will exploit this rich dataset in combination with ground based spectroscopy and time delays to determine quantities such as the Hubble constant, the free streaming length of dark matter, and the normalization of the initial stellar mass function. △ Less

Submitted 3 September, 2020; v1 submitted 24 July, 2018; originally announced July 2018.

Comments: 22 pages, 9 figures, 8 tables, Accepted to MNRAS. This version: updated Table 4 from the erratum

Journal ref: MNRAS 483 (2019) 5649

A precise extragalactic test of General Relativity

Authors: Thomas E. Collett, Lindsay J. Oldham, Russell J. Smith, Matthew W. Auger, Kyle B. Westfall, David Bacon, Robert C. Nichol, Karen L. Masters, Kazuya Koyama, Remco van den Bosch

Abstract: Einstein's theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens, ESO 325-G004, provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, $γ$. By reconstructing the observed light profile of the le… ▽ More Einstein's theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens, ESO 325-G004, provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, $γ$. By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that $γ= 0.97 \pm 0.09$ at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity. △ Less

Submitted 21 June, 2018; originally announced June 2018.

Comments: Published in Science. 42 pages, 10 figures including supplementary text and figures