arXiv subjects

S. H. Suyu

Publications and source records attributed to S. H. Suyu.

At least 19 recordsLinked to original sources

arXiv2026

TDCOSMO XXVIII. The Hubble constant from the quadruply lensed quasar J1537$-$3010 with precise time delays

We present the first measurement of the Hubble constant ($H_0$) from the quadruply-lensed quasar J1537$-$3010, which has optically-measured time delays at $\sim2 \%$ precision. We combine these delays with multi-band imaging data from the Hubble Space Telescope (HST) and model the system with two independent software and teams. We adopt a mass profile that is maximally degenerate with $H_0$ to fully incorporate the mass-sheet degeneracy in the error budget, with nuisance parameters constrained by spatially resolved stellar kinematics from the Multi Unit Spectroscopic Explorer (MUSE) and a line-of-sight (LoS) analysis using the Euclid Flagship simulation. The entire analysis is performed blindly to $H_0$, distances and mass density slope of the main deflector. After unblinding, we measure $H_0 = 75.5^{+9.3}_{-5.8}\ {\rm km\,s^{-1}\,Mpc^{-1}}$, corresponding to a $10\%$ precision measurement from a single system. This precision is driven by conservative lens modeling assumptions including differences between lens modeling methods and the limited stellar kinematics constraints, from which we infer a total mass-sheet parameter $λ\equiv(1-κ_{\rm ext})λ_{\rm int} = 0.89^{+0.11}_{-0.06}$ ($λ_{\rm int}=0.89^{+0.09}_{-0.07}$) that is consistent with current results for elliptical galaxies ($λ\approx 1$). Our lensing constraints, stellar kinematic measurements and LoS characterization will be included in subsequent population-level measurements of $H_0$. Moreover, our lens models combined with future near-infrared spectroscopy and imaging from the James Webb Space Telescope will further reduce the uncertainties on $H_0$ from J1537$-$3010 alone, bringing it closer to the few percents precision of the time delays.

astro-ph.CO↗

arXiv2026

HOLISMOKES -- XVIII. Cosmology with strongly lensed type II supernovae: Effects of instrumental setups on $H_0$

The upcoming Rubin Observatory and subsequent follow-up observations should improve the determination of the Hubble constant ($H_0$) via time-delay cosmography of strongly lensed type II supernovae (LSNe II), by enabling the detection of many more such events. In our previous work, we developed a method for determining the supernova (SN) phase from spectral absorption features. Because obtaining spectra of faint targets such as distant SN II is expensive, we examined how low-resolution spectra influence the precision of time-delay retrieval, and consequently the precision on $H_0$. We considered spectral resolutions $R = \fracλ{Δλ}$ between 100 and 250, and we investigated three signal-to-noise ratio ($S/N$) values of 10, 15, and 20, for each resolution. Furthermore, we forecast the precision on $H_{0}$ achievable with $S/N=10$ and compared the observing time required to reach it with ground-based and space-based facilities. We find that the time delay can be determined without bias and with uncertainties as low as 1.3 days for the investigated resolutions and $S/N$ values when we combine time-delay measurements of multiple absorption lines. For a typical LSN II system (absolute magnitude $\sim-$17 mag in the rest-frame V band, source redshift of \zs = 0.8), the required exposure times range from multiple hours for ground-based observations to a few minutes for space-based observations with the JWST. Our predictions on the precision of $H_0$ for a single lensed SN range from 14.2\% for $R = 100$ and $S/N$ = 10 to 7.5\% for $R = 250$ and $S/N$ = 20, enabling a 1\% determination of $H_0$ from $\sim$20 lensed SNe in the coming years.

astro-ph.CO↗

arXiv2026

A new $H_0$ measurement with SNe Requiem and Encore using $\texttt{Gravity.jl}$

We present a strong-lensing (SL) analysis of the galaxy cluster MACS J0138.0-2155 (z=0.336), the first known lens cluster discovered to host two distinct multiply imaged Type Ia supernovae (SNe): SN Requiem and SN Encore. Both SNe are located in the massive, multiply imaged red galaxy MRG-M0138 at z=1.949. The projected total mass of this cluster has been investigated with several independent lens models (Suyu+26; Pierel+26), using a sample of 23 spectroscopically confirmed multiple images from 8 background sources (0.767 10%). The forthcoming reappearance of SN Requiem offers an immediate opportunity to significantly improve constraints on H0, provided that lens-model systematics are controlled. These results establish M0138 as a premier anchor for high-precision cluster-scale TDC.

astro-ph.CO↗

arXiv2026

Strong Lensing Model and Dust Extinction Maps of the Host Galaxy of Type Ia Supernova H0pe

Strong gravitational lensing by massive galaxy clusters offers rare opportunities to observe multiple images of distant ($z \gtrsim 2$) Type Ia supernovae (SNe) and to resolve the properties of their host galaxies. A recent outstanding example is the Type Ia SN H0pe ($z = 1.78$), which the James Webb Space Telescope (JWST) discovered in NIRCam images, when the galaxy cluster PLCK G165.7+67.0 (G165, $z = 0.35$) still produced three images of it. In this work, we build a new strong lensing model of G165, first using only the positions of multiple images of background galaxies. We then significantly increase the number of constraints around the position of SN H0pe by modeling the extended surface brightness of the SN host galaxy. Including extended image information reduces the average uncertainty on mass model parameters by more than an order of magnitude. We also study the spatial distribution of dust in the arc to estimate the dust extinction at the position of SN H0pe. We find good statistical agreement of the extinction estimate, at $\lesssim 1σ$, with three fully independent methods based on spectral energy distribution fitting. Moreover, our extended-image lens model of G165 allows us to map the dust distribution of the host galaxy from the image plane to the source plane. Supernova H0pe exploded in a region with a relatively high extinction ($A_V \approx 0.9$ mag) at around $\sim 1$ kpc from its host center. This work shows that extended image modeling in lensing clusters simultaneously reduces the uncertainty on lens model parameters and enables spatially resolved analyses of lensed transients' host galaxies. Such modeling advances are expected to play an important role in future cosmological analyses using strongly lensed SNe.

astro-ph.GA↗

arXiv2026

Cosmology with supernova Encore in the strong lensing cluster MACS J0138-2155: Lens model comparison and H0 measurement

MACS J0138-2155 is the only known cluster to strongly lens two supernovae (SNe), Requiem and Encore, from the same host galaxy at z=1.949. We present seven independent mass models of the galaxy cluster built using six software packages. By conducting a blind analysis (no exchanges of results between modeling teams), we quantified uncertainties due to modeling and software. Through HST, JWST and MUSE observations, we assembled high-quality data products, including eight "gold" lensed image systems consisting of 23 images with secure spectroscopic redshifts, and one "silver" system with a likely redshift value. Restricting to the gold images, we obtain overall consistent model predictions of the positions, magnifications and time delays of SN Encore and SN Requiem images, especially for models with $χ^2 \leq 25$. We predict the appearance of the next images of SNe Encore and Requiem with a time delay of >~3000 days and of ~3700 to 4000 days, respectively, based on a fiducial cosmological model of $H_0 = 70 {\rm\ km\ s^{-1}\ Mpc^{-1}}$ and $Ω_{\rm m} = 0.3$. We obtain relations between $H_0$ and the time delays of SNe Encore and Requiem. In particular, for $H_0 = 73 {\rm\ km\ s^{-1}\ Mpc^{-1}}$, the four lowest $χ^2$ models predict SN Requiem to reappear in ~Apr-Dec 2026; for $H_0 = 67 {\rm\ km\ s^{-1}\ Mpc^{-1}}$, in ~Mar-Nov 2027. Using the newly measured time delay between the two detected images of SN Encore by Pierel et al. (2026) and our mass models, we jointly infer $H_0 = {\rm 66.9^{+11.2}_{-8.1}\ km\ s^{-1}\ Mpc^{-1}}$, where the uncertainty is dominated by that of the time delay. The long delays of the next-appearing SN Requiem and SN Encore images provide excellent opportunities to measure $H_0$ with an uncertainty of 2-3%. Our mass models form the basis for cosmological inference from this unique lens cluster with two strongly lensed SNe. (Abridged)

astro-ph.CO↗

arXiv2026

HOLISMOKES XX. Lens models of binary lens galaxies with five images of Supernova Winny

Strongly lensed supernovae (SNe) provide a powerful way to study cosmology, SNe and galaxies. Modelling the lens system is key to extracting astrophysical and cosmological information. We present adaptive-optics-assisted high-resolution images of SN Winny (SN 2025wny) in the J and K filters obtained with the Large Binocular Telescope (LBT). The LBT imaging confirms the presence of a fifth point source, whose colour is consistent with that of the other SN images at similar phases, while lens modelling robustly supports its interpretation as an additional image of SN~Winny. We measure the positions of the five SN images with uncertainties varying between 1 and 14 milliarcseconds. We build the first mass models using lenstronomy and GLEE, and explore three classes of mass models for the two lens galaxies G1 and G2. The optimal model class of the three is a singular isothermal ellipsoid for G1, a singular isothermal sphere for G2, and an external shear. We infer the enclosed masses within the Einstein radius as 4.61^{+0.06}_{-0.04} \times 10^{11}\,M_\odot for G1 and 1.01\pm0.02 \times 10^{11}\,M_\odot for G2. The lensing configuration by the two lens galaxies can produce two additional magnified SN images beyond the five observed ones; the exclusion of such model configurations further constrains the lens model parameters. Our model fits to the observed image positions with an RMS of ~0.0012" - 0.0025", within the observed positional uncertainties. The predicted magnifications of the multiple images vary between ~1.6 (for the faintest fifth image E) to ~10 (for the brightest image A). The predicted relative lensing magnifications of the multiple images do not match that of the observed within 2σuncertainties. The differences in the relative magnifications could be due to millilensing/microlensing. Our mass models form the basis for future analyses of this unique system. (abridged)

astro-ph.GA↗

arXiv2026

A boost in the precision of cluster-mass models: Exploiting the extended surface brightness of the lensed supernova Refsdal host galaxy

Combining deep Hubble Space Telescope (HST) images and extensive data from the Multi-Unit Spectroscopic Explorer, we present new mass models of the cluster MACS J1149.5+2223, strongly lensing the supernova (SN) Refsdal, fully exploiting the source surface-brightness distribution of the SN host for the first time. In detail, we incorporated 77,000 HST pixels, in addition to the known 106 point-like multiple images, in our modeling. We considered four different models to explore the effect of the relative weighting of the point-like multiple image positions and flux distribution of the SN host on the model optimization. When the SN host's extended image is included, we find that the statistical uncertainties of all 34 free model parameters are reduced by factors ranging from one to two orders of magnitude compared to the statistical uncertainty of the point-like only model, irrespective of the adopted different image weights. We quantified the remarkably increased level of precision with which the cluster's total mass and the predicted time delays of the SN Refsdal multiple image positions can be reconstructed. We also show the delensed image of the SN host, a spiral galaxy at zSN = 1.49, in multiple HST bands. In all those applications, we obtain a significant reduction of the statistical uncertainty, which is now below the level of even the small systematic uncertainty on the mass model that could be assessed by the different approaches. These results demonstrate that with extended image models of lensing clusters it is possible to measure the cluster's total mass distribution, the values of the cosmological parameters, and the physical properties of high-redshift sources with an unparalleled precision, making the typically not-quantified systematic uncertainties now crucial.

astro-ph.CO↗

arXiv2026

Rates of Strongly Lensed Tidal Disruption Events

In the coming years, surveys such as the Rubin Observatory's Legacy Survey of Space and Time (LSST) are expected to increase the number of observed Tidal Disruption Events (TDEs) substantially. We employ Monte Carlo integration to calculate the unlensed and lensed TDE rate as a function of limiting magnitude in $u$, $g$, $r$, and $i$-bands. We investigate the impact of multiple luminosity models, black hole mass functions (BHMFs), and flare temperatures on the TDE rate. Notably, this includes a semi-analytical model, which enables the determination of the TDE temperature in terms of black hole (BH) mass. We predict the highest unlensed TDE rate to be in $g$-band. It ranges from $16$ to $5,440\;\mathrm{yr}^{-1}\;(20,000\;\mathrm{deg}^2)^{-1}$ for the Zwicky Transient Facility, being more consistent with the observed rate at the low end. For LSST, we expect a rate in $g$-band between $3,580$ and $82,060\;\mathrm{yr}^{-1}\;(20,000\;\mathrm{deg}^2)^{-1}$. A higher theoretical prediction is understandable, as we do not consider observational effects such as completeness. The unlensed and lensed TDE rates are insensitive to the redshift evolution of the BHMF, even for LSST limiting magnitudes. The best band for detecting lensed TDEs is also $g$-band. Its predicted rates range from $0.43$ to $15\;\mathrm{yr}^{-1}\;(20,000\;\mathrm{deg}^2)^{-1}$ for LSST. The scatter of predicted rates reduces when we consider the fraction of lensed TDEs; that is, a few in ten thousand TDEs will be lensed. Despite the large scatter in the rates of lensed TDEs, our comprehensive considerations of multiple models suggest that lensed TDEs will occur in the $10$-year LSST lifetime, providing an exciting prospect for detecting such events. We expect the median redshift of a lensed TDE to be between $1.5$ and $2$. In this paper, we additionally report on lensed TDE properties, such as the BH mass and time delays.

astro-ph.HE↗

arXiv2025

Cosmology with supernova Encore in the strong lensing cluster MACS J0138$-$2155: photometry, cluster members, and lens mass model

The strongly lensed Supernova (SN) Encore at a redshift of $z = 1.949$, discovered behind the galaxy cluster MACS J0138$-$2155 at $z=0.336$, provides a rare opportunity for time-delay cosmography and studies of the SN host galaxy, where previously another SN, called SN Requiem, had appeared. To enable these studies, we combine new James Webb Space Telescope (JWST) imaging, archival Hubble Space Telescope (HST) imaging, and new Very Large Telescope (VLT) spectroscopic data to construct state-of-the-art lens mass models that are composed of cluster dark-matter (DM) halos and galaxies. We determine the photometric and structural parameters of the galaxies across six JWST and five HST filters. We use the color-magnitude and color-color relations of spectroscopically-confirmed cluster members to select additional cluster members, identifying a total of 84 galaxies belonging to the galaxy cluster. We construct seven different mass models using a variety of DM halo mass profiles, and explore both multi-plane and approximate single-plane lens models. As constraints, we use the observed positions of 23 multiple images from eight multiply lensed sources at four distinct spectroscopic redshifts. In addition, we use stellar velocity dispersion measurements to obtain priors on the galaxy mass distributions. We find that six of the seven models fit well to the observed image positions. Mass models with cored-isothermal DM profiles fit well to the observations, whereas the mass model with a Navarro-Frenk-White cluster DM profile has an image-position $χ^2$ value that is four times higher. We build our ultimate model by combining four multi-lens-plane mass models and predict the image positions and magnifications of SN Encore and SN Requiem. Our work lays the foundation for building state-of-the-art mass models of the cluster for future cosmological analysis and SN host galaxy studies.

astro-ph.CO↗

arXiv2025

Cosmology with supernova Encore in the strong lensing cluster MACS J0138-2155: Time delays & Hubble constant measurement

Multiply-imaged supernovae (SNe) provide a novel means of constraining the Hubble constant ($H_0$). Such measurements require a combination of precise models of the lensing mass distribution and an accurate estimate of the relative time delays between arrival of the multiple images. Only two multiply-imaged SNe, Refsdal and H0pe, have enabled measurements of $H_0$ thus far. Here we detail the third such measurement for SN Encore, a $z=1.95$ SNIa discovered in JWST/NIRCam imaging. We measure the time delay, perform simulations of additional microlensing and millilensing systematics, and combine with the mass models of Suyu et al. in a double-blind analysis to obtain our $H_0$ constraint. Our final time-delay measurement is $Δt_{1b,1a}=-39.8_{-3.3}^{+3.9}$ days, which is combined with seven lens models weighted by the likelihood of the observed multiple image positions for a result of $H_0=66.9_{-8.1}^{+11.2} \rm{km} \rm{s}^{-1}\rm{Mpc}^{-1}$. The uncertainty on this measurement could be improved significantly if template imaging is obtained. Remarkably, a sibling to SN Encore (SN "Requiem") was discovered in the same host galaxy, making the MACS J0138.0-2155 cluster the first system known to produce more than one observed multiply-imaged SN. SN Requiem has a fourth image that is expected to appear within a few years, providing an unprecedented decade-long baseline for time-delay cosmography and an opportunity for a high-precision joint estimate of $H_0$.

astro-ph.CO↗

arXiv2025

HOLISMOKES XVI: Lens search in HSC-PDR3 with a neural network committee and post-processing for false-positive removal

We have carried out a systematic search for galaxy-scale lenses exploiting multi-band imaging data from the third public data release of the Hyper Suprime-Cam (HSC) survey with the focus on false-positive removal, after applying deep learning classifiers to all 110 million sources with i-Kron radius above 0.8". To improve the performance, we tested the combination of multiple networks from our previous lens search projects and found the best performance by averaging the scores from five of our networks. Although this ensemble network leads already to a false-positive rate (FPR) of 0.01% at a true-positive rate (TPR) of 75% on known real lenses, we have elaborated techniques to further clean the network candidate list before visual inspection. In detail, we tested the rejection using SExtractor and the modeling network from HOLISMOKES IX, which resulted together in a candidate rejection of 29% without lowering the TPR. We carried out a comprehensive multi-stage visual inspection involving eight individuals and identified 95 grade A (average grade G >2.5) and 503 grade B (2.5 >G >1.5) lens candidates, including 92 discoveries reported for the first time. This inspection also incorporated a novel environmental characterization using histograms of photometric redshifts. We publicly release the average grades, mass model predictions, and environment characterization of all visually inspected candidates, while including references for previously discovered systems, which makes this catalog one of the largest compilation of known lenses. The results demonstrate that (1) the combination of multiple networks enhances the selection performance and (2) both automated masking tools as well as modeling networks, which can be easily applied to hundreds of thousands of network candidates, help reduce the number of false positives that is the main limitation in lens search to date.

astro-ph.IM↗

arXiv2025

Cosmology with Supernova Encore in the lensing cluster MACS J0138$-$2155 -- Spectroscopy with MUSE

We present a spectroscopic analysis of MACS J0138$-$2155, at $z=0.336$, the first galaxy cluster hosting two strongly-lensed supernovae (SNe), Requiem and Encore, providing us with a chance to obtain a reliable $H_0$ measurement from the time delays between the multiple images. We take advantage of new data from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope, covering a central $1 \rm \, arcmin^2$ of the lensing cluster, for a total depth of 3.7 hours, including 2.9 hours recently obtained by our Target of Opportunity programme. Our new spectroscopic catalogue contains reliable redshifts for 107 objects, including 50 galaxy cluster members with secure redshift values in the range $0.324 < z < 0.349$, and 13 lensed multiple images from four background sources between $0.767\leq z \leq 3.420$, including four images of the host galaxy of the two SNe. We exploit the MUSE data to study the stellar kinematics of 14 bright cluster members and two background galaxies, obtaining reliable measurements of their line-of-sight velocity dispersion. Finally, we combine these results with measurements of the total magnitude of the cluster members in the Hubble Space Telescope F160W band to calibrate the Faber-Jackson relation between luminosity and stellar velocity dispersion ($L \propto σ^{1/α}$) for the early-type cluster member galaxies, measuring a slope $α=0.25^{+0.05}_{-0.05}$. A pure and complete sample of cluster member galaxies and a reliable characterisation of their total mass structure are key to building accurate total mass maps of the cluster, mitigating the impact of parametric degeneracies, which is necessary for inferring the value of $H_0$ from the measured time delays between the lensed images of the two SNe.

astro-ph.GA↗

arXiv2025

Euclid: The Early Release Observations Lens Search Experiment

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.

astro-ph.GA↗

arXiv2025

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

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.

astro-ph.GA↗

arXiv2024

HOLISMOKES XV. Search for strong gravitational lenses combining ground-based and space-based imaging

In the past, researchers have mostly relied on single-resolution images from individual telescopes to detect gravitational lenses. We propose a search for galaxy-scale lenses that, for the first time, combines high-resolution single-band images (in our case the Hubble Space Telescope, HST) with lower-resolution multi-band images (in our case Legacy survey, LS) using machine learning. This methodology aims to simulate the operational strategies that will be employed by future missions, such as combining the images of Euclid and the Rubin Observatory's Legacy Survey of Space and Time (LSST). To compensate for the scarcity of lensed galaxy images for network training, we have generated mock lenses by superimposing arc features onto HST images, saved the lens parameters, and replicated the lens system in the LS images. We test four architectures based on ResNet-18: (1) using single-band HST images, (2) using three bands of LS images, (3) stacking these images after interpolating the LS images to HST pixel scale for simultaneous processing, and (4) merging a ResNet branch of HST with a ResNet branch of LS before the fully connected layer. We compare these architecture performances by creating Receiver Operating Characteristic (ROC) curves for each model and comparing their output scores. At a false-positive rate of $10^{-4}$, the true-positive rate is $\sim$0.41, $\sim$0.45, $\sim$0.51 and $\sim$0.55, for HST, LS, stacked images and merged branches, respectively. Our results demonstrate that models integrating images from both the HST and LS significantly enhance the detection of galaxy-scale lenses compared to models relying on data from a single instrument. These results show the potential benefits of using both Euclid and LSST images, as wide-field imaging surveys are expected to discover approximately 100,000 lenses.

astro-ph.IM↗

arXiv2024

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

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.

astro-ph.IM↗

arXiv2024

Cosmography from accurate mass modeling of the lens group SDSS J0100+1818: five sources at three different redshifts

Systems where multiple sources at different redshifts are strongly lensed by the same deflector allow one to directly investigate the evolution of the angular diameter distances with redshift, and thus to learn about the geometry of the Universe. We present measurements of the values of the total matter density, $Ω_m$, and of the dark energy equation of state parameter, $w$, through a strong lensing analysis of SDSSJ0100+1818, a group-scale system at $z=0.581$ with five lensed sources, from $z=1.698$ to $4.95$. We use new MUSE data to securely measure the redshift of 65 sources, including the five multiply imaged background sources (lensed into a total of 18 multiple images) and 19 galaxies on the deflector plane (the brightest group galaxy, BGG, and 18 fainter members), all employed to build robust strong lensing models with the software GLEE. We measure $Ω_m = 0.14^{+0.16}_{-0.09}$ in a flat $Λ$ cold dark matter (CDM) model, and $Ω_m = 0.19^{+0.17}_{-0.10}$ and $w=-1.27_{-0.48}^{+0.43}$ in a flat $w$CDM model. We quantify, through a multi-plane approach, the impact of different sources angularly close in projection on the inferred values of the cosmological parameters. We obtain consistent median values, with uncertainties for only $Ω_m$ increasing by a factor of 1.5. We accurately measure a total mass of $(1.55 \pm 0.01) \times 10^{13}$ M$_\odot$ within 50 kpc and a stellar over total mass profile decreasing from $45.6^{+8.7}_{-8.3}\%$ at the BGG effective radius to $(6.6\pm 1.1)\%$ at $R\approx 77$ kpc. Our results confirm that SDSSJ0100+1818 is one of the most massive (lens) galaxies known at intermediate redshift and that group-scale systems that act as lenses for $\geq 3$ background sources at different redshifts enable to estimate the values of the cosmological parameters with an accuracy that is competitive with that obtained from lens galaxy clusters.

astro-ph.CO↗

arXiv2024

J1721+8842: The first Einstein zig-zag lens

We report the discovery of the first example of an Einstein zig-zag lens, an extremely rare lensing configuration. In this system, J1721+8842, six images of the same background quasar are formed by two intervening galaxies, one at redshift $z_1 = 0.184$ and a second one at $z_2 = 1.885$. Two out of the six multiple images are deflected in opposite directions as they pass the first lens galaxy on one side, and the second on the other side -- the optical paths forming zig-zags between the two deflectors. In this letter, we demonstrate that J1721+8842, previously thought to be a lensed dual quasar, is in fact a compound lens with the more distant lens galaxy also being distorted as an arc by the foreground galaxy. Evidence supporting this unusual lensing scenario includes: 1- identical light curves in all six lensed quasar images obtained from two years of monitoring at the Nordic Optical Telescope; 2- detection of the additional deflector at redshift $z_2 = 1.885$ in JWST/NIRSpec IFU data; and 3- a multiple-plane lens model reproducing the observed image positions. This unique configuration offers the opportunity to combine two major lensing cosmological probes: time-delay cosmography and dual source-plane lensing since J1721+8842 features multiple lensed sources forming two distinct Einstein radii of different sizes, one of which being a variable quasar. We expect tight constraints on the Hubble constant and the equation of state of dark energy by combining these two probes on the same system. The $z_2 = 1.885$ deflector, a quiescent galaxy, is also the highest-redshift strong galaxy-scale lens with a spectroscopic redshift measurement.

astro-ph.CO↗