Sherry H. Suyu

The internal mass structure of elliptical galaxies offers critical insights into galaxy formation, yet disentangling stellar mass from dark matter (DM) and determining the stellar initial mass function (IMF) remain challenging. We present a detailed analysis of ESO0286-G022 ( z = 0.0312), a rare nearby strong-lens system with a fast-rotating elliptical galaxy, combining high-resolution Hubble Space Telescope (HST) imaging with VLT/MUSE integral-field stellar kinematics. We constructed a series of axisymmetric and triaxial Schwarzschild orbit-superposition models to reconstruct its intrinsic shape and mass distribution. We find that despite being a fast rotator, ESO0286 exhibits clear kinematic signatures of intrinsic triaxiality, characterized by rotation along both the major and minor axes, making it only the second such confirmed case. Models based on kinematics alone yield significantly larger scatter in the predicted total mass at large radii. By incorporating the mass enclosed within the Einstein radius from strong lensing as a complementary constraint to the kinematic data, we were able to anchor the total mass at a radius where the constraints taken from the IFU data alone are weak. This allowed us to significantly reduce the uncertainty on the outer mass profile and orbital structure, establishing that only models with strong radial anisotropy beyond the IFU FoV are compatible with the lensing constraints. In the inner regions, we robustly constrained an upper limit for the stellar mass around r ∼ 0.7 kpc, ruling out an IMF more bottom-heavy than Kroupa. The data allowed for a gentle gradient toward a slightly more bottom-heavy central IMF. This result is well aligned with recent dynamical studies of local well-resolved massive early-type galaxies; however, it stands in contrast to the heavier IMFs reported for lenses detected at z > 0.1. Our work demonstrates the power of combining lensing and dynamical modeling to resolve the detailed inner structure of massive galaxies.

The multiply imaged SN 2022riv was discovered through a search of galaxy cluster fields as part of a Hubble Space Telescope (HST) SNAP program to find highly magnified stars. The supernova (SN) was detected in the image corresponding to the longest time delay of a galaxy at redshift z = 1.522, strongly lensed by the foreground galaxy cluster RX J2129.7+0005. Follow up James Webb Space Telescope (JWST) NIRSpec G140M and PRISM spectroscopy yields an SN Ia classification. Using the SALT3-NIR light-curve fitter, we obtain a cosmology-independent measurement of the magnification of 5.35 ± 1.01 for the last-to-arrive image of the SN, with multiple SALT SN spectral time-series models yielding consistent constraints. The last-to-arrive image of SN 2022riv we detect appeared adjacent to the brightest cluster galaxy (BCG) at a location with an exceptionally high stellar mass density (∼1–2 dex higher than that of SN Refsdal), where microlensing is expected to introduce a 20%–50% modulation of the magnification. Analyzing six independent lens models of the cluster, we find that four predict the magnification with much greater precision ( p < 0.05) than would be expected by random chance, given the large effect anticipated from microlensing. Five models yield magnifications of roughly 4–7 (within 1 σ ) prior to accounting for microlensing, whereas HoliGRALE favors a significantly higher value of 15.39 ± 0.85. After incorporating nominal microlensing, the HoliGRALE prediction is within 1 σ tension with our measurement. A companion paper will present constraints on the relative time delay of the image that arrived earlier.

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 = λ /Δ λ 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 ∼−17 mag in the rest-frame V band, source redshift of z _s = 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 ∼20 lensed SNe in the coming years.

Supermassive black holes and their host galaxies grow together over time, producing correlations between the black hole mass and various galaxy properties. Determining the evolution of these correlations requires precise measurements of the masses of distant black holes. We observed the gravitationally lensed quiescent galaxy MRG-M0138 at redshift 1.95 using James Webb Space Telescope integral field spectroscopy to spatially resolve the kinematics of stars within the black hole’s sphere of influence. By using a foreground lens model and fitting stellar dynamical models, we determined the mass of its inactive black hole to be M • = 6.0 − 1.7 + 2.1 × 10 9 solar masses. Comparing this measurement to local galaxies, we found that M • is higher than expected given the galaxy’s bulge mass but consistent with the correlation of M • with stellar velocity dispersion.

Strong gravitational lensing by massive galaxy clusters offers rare opportunities to observe multiple images of distant ( z ≳ 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 ≲1 σ , 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 ≈ 0.9 mag) at around ∼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.

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 z _SN = 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.

Spatially resolved stellar kinematics has become a key ingredient in time-delay cosmography to break the mass-sheet degeneracy in the mass profile and in turn provide a precise constraint on the Hubble constant and other cosmological parameters. In this paper, we present the first measurements of 2D resolved stellar kinematics for the lens galaxy in the quadruply lensed quasar system RXJ1131−1231 using integral field spectroscopy from JWST’s Near-Infrared Spectrograph (NIRSpec), marking the first such measurement conducted with JWST. In extracting robust kinematic measurements from this first-of-its-kind dataset, we have made methodological improvements both in the data reduction and kinematic extraction. In our kinematic extraction procedure, we performed joint modeling of the lens galaxy, the quasar, and its host galaxy’s contributions in the spectra to deblend the lens galaxy component and robustly constrain its stellar kinematics. Our improved methodological frameworks are released as software pipelines for future use: SQUIRREL , for extracting stellar kinematics, and R EGAL J UMPER , for JWST-NIRSpec data reduction. We incorporated additional artifact cleaning beyond the standard JWST pipeline. We compared our measured stellar kinematics from the JWST NIRSpec with previously obtained ground-based measurements from the Keck Cosmic Web Imager integral field unit and find that the two datasets are statistically consistent at a ∼1.1 σ confidence level. Our measured kinematics will be used in a future study to improve the precision of the Hubble constant measurement.

Strong gravitationally lensed supernovae (LSNe), though rare, are exceptionally valuable probes for cosmology and astrophysics. Upcoming time-domain surveys such as the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST) offer a major opportunity to discover large number of LSNe. Early identification is crucial for timely follow-up observations. We have developed a deep learning pipeline to detect LSNe using multiband, multi-epoch image cutouts. Our model is based on a 2D convolutional long short-term memory ( ConvLSTM2D ) architecture designed to capture both spatial and temporal correlations in time-series imaging data. Predictions are made after each observation in the time series, with accuracy expected to improve progressively as additional data are processed. We trained the model on realistic simulations derived from Hyper Suprime-Cam (HSC) data, which closely matches LSST in depth and filter characteristics. In this work, we focus exclusively on Type Ia supernovae (SNe Ia). LSNe Ia were injected into HSC luminous red galaxies (LRGs) at various phases of evolution to create positive examples of LSNe Ia time series. Negative examples include variable sources observed in the HSC Transient Survey (including unclassified transients) and simulated unlensed SNe Ia in LRG and spiral galaxies. Our multiband model shows rapid classification performance improvements during the initial few observations and quickly reaches a high detection efficiency: At a fixed false-positive rate (FPR) of 0.01%, the true-positive rate (TPR) reaches ≳60% by the seventh observation and exceeds ≳70% by the ninth observation. If we relax the FPR to 0.1%, the TPR reaches close to 60% as early as the fourth observation. Although the single-band analysis performs reasonably well in isolation, the multiband model significantly outperforms it, particularly in the early stages, by building a richer memory and leveraging color information. Among the negative examples, SNe in LRGs remain the primary source of FPR, as they can resemble their lensed counterparts under certain conditions. Additionally, the model detects quads more effectively than doubles, and it performs better on systems with larger image separations. Although we trained and tested the model on HSC-like data, our approach is applicable to any cadenced imaging survey – particularly LSST, where the higher expected cadence (five to ten times that of HSC) should further boost performance.

Time-delay cosmography leverages strongly lensed quasars to measure the Universe’s current expansion rate, H ₀ , independently from other methods. The latest TDCOSMO milestone measurement primarily used quadruply lensed quasars for their mass profile constraints. However, doubly lensed quasars, being more abundant and offering precise time delays, could expand the sample by a factor of 5, significantly advancing towards a 1% precision measurement of H ₀ . We present the first TDCOSMO analysis of a doubly imaged source, HE 1104−1805, including the measurement of the four necessary ingredients. First, by combining 17 years of data from the SMARTS, Euler, and WFI telescopes, we measured a time delay of 176.3 ^+11.4 _−10.3 days. Second, using MUSE data, we extracted stellar velocity dispersion measurements in three radial bins with 5% to 13% precision. Third, employing F160W HST imaging for lens modelling and marginalising over various modelling choices, we measured the Fermat potential difference between the images. Fourth, using wide-field imaging, we measured the convergence added by objects not included in the lens modelling. By combining these four ingredients, we measured the time delay distance and the angular diameter distance to the deflector, favouring a power-law mass model over a baryonic and dark matter composite model. The measurement was performed blindly to prevent experimenter bias and resulted in a Hubble constant of H ₀ = ^+5.8 _−5.0 × λ _int km s ⁻¹ Mpc ⁻¹ , where λ _int is the internal mass sheet degeneracy parameter. This is in agreement with the TDCOSMO-2025 milestone and its precision for λ _int = 1 is comparable to that obtained with the best-observed quadruply lensed quasars (4–6%). This work is a stepping stone towards a precise measurement of H ₀ using a large sample of doubly lensed quasars, supplementing the current sample. The next TDCOSMO milestone paper will include this system in its hierarchical analysis, constraining λ _int and H ₀ jointly with multiple lenses.