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Abstract The first James Webb Space Telescope (JWST) Near InfraRed Camera imaging in the field of the galaxy cluster PLCK G165.7+67.0 (z= 0.35) uncovered a Type Ia supernova (SN Ia) atz= 1.78, called “SN H0pe.” Three different images of this one SN were detected as a result of strong gravitational lensing, each one traversing a different path in spacetime, thereby inducing a relative delay in the arrival of each image. Follow-up JWST observations of all three SN images enabled photometric and rare spectroscopic measurements of the two relative time delays. Following strict blinding protocols which oversaw a live unblinding and regulated postunblinding changes, these two measured time delays were compared to the predictions of seven independently constructed cluster lens models to measure a value for the Hubble constant,H₀ =  71.8 + 9.2 − 8.1 km s⁻¹Mpc⁻¹. The range of admissibleH₀values predicted across the lens models limits further precision, reflecting the well-known degeneracies between lens model constraints and time delays. It has long been theorized that a way forward is to leverage a standard candle, but this has not been realized until now. For the first time, the lens models are evaluated by their agreement with the SN absolute magnifications, breaking degeneracies and producing our best estimate,H₀ =  ${75.7}_{-5.5}^{+8.1}$km s⁻¹Mpc⁻¹. This is the first precise measurement ofH₀from a multiply imaged SN Ia and only the second from any multiply imaged SN. 

Abstract We present the most detailed spectrum of intracluster light (ICL) in an individual cluster to date, the relaxed system RX J2129.7+0005, atz∼ 0.234. Using 15 broadband, deep images observed with the Hubble Space Telescope and JWST in the optical and the infrared, plus deep integral field spectroscopy from MUSE, we computed a total of 3696 ICL maps spanning the spectral range ∼0.4−5μm with our algorithm CICLE, a method that is extremely well suited to analyzing large samples of data in a fully automated way. We used both parametric and nonparametric approaches to fit the spectral energy distribution of the ICL and infer its physical properties, yielding a stellar mass ${\log }_{10}\left(M_{*}/M_{\odot }\right)$between 11.5 and 12.7 and an average age between 9.7 and 10.5 Gyr, from CIGALE and Prospector results. This implies that the ICL in RX J2129.7+0005 is, on average, older than that of disturbed clusters, suggesting that the contribution from different stellar populations to the ICL is at play depending on the cluster’s dynamical state. Coupled with X-ray observations of the hot gas distribution, we confirm the relaxed state of RX J2129.7+0005, showing clear signs of sloshing after a last major merger with a high-mass-ratio satellite that could have happened ∼6.6 Gyr ago in a relatively radial orbit. The presence of substructure in the ICL, such as shells, clouds with different densities and a certain degree of boxyness, and a clump, supports this scenario. 

Abstract Galaxy-cluster gravitational lenses enable the study of faint galaxies even at large lookback times, and, recently, time-delay constraints on the Hubble constant. There have been few tests, however, of lens model predictions adjacent to the critical curve (≲8″) where the magnification is greatest. In a companion paper, we use the GLAFIC lens model to constrain the BalmerL–σrelation for Hiiregions in a galaxy at redshiftz= 1.49 strongly lensed by the MACS J1149 galaxy cluster. Here we perform a detailed comparison between the predictions of 10 cluster lens models that employ multiple modeling assumptions with our measurements of 11 magnified, giant Hiiregions. We find that that the models predict magnifications an average factor of 6.2 smaller, a ∼2σtension, than that inferred from the Hiiregions under the assumption that they follow the low-redshiftL–σrelation. To evaluate the possibility that the lens model magnifications are strongly biased, we next consider the flux ratios among knots in three images of Sp1149, and find that these are consistent with model predictions. Moreover, while the mass-sheet degeneracy could in principle account for a factor of ∼6 discrepancy in magnification, the value ofH₀inferred from SN Refsdal’s time delay would become implausibly small. We conclude that the lens models are not likely to be highly biased, and that instead the Hiiregions in Sp1149 are substantially more luminous than the low-redshift BalmerL–σrelation predicts. 

Abstract A bright (m_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 ∼10 yr window to be ≈3%. These observations have the potential to yield a Hubble constant (H₀) measurement with ∼10% 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 ∼2030, providing an unprecedented baseline for time-delay cosmography. 

Abstract Dark matter subhalos with extended profiles and density cores, and globular star clusters of mass 10⁶–10⁸M_⊙that live near the critical curves in galaxy cluster lenses can potentially be detected through their lensing magnification of stars in background galaxies. In this work, we study the effect such subhalos have on lensed images, and compare to the case of more well-studied microlensing by stars and black holes near critical curves. We find that the cluster density gradient and the extended mass distribution of subhalos are important in determining image properties. Both lead to an asymmetry between the image properties on the positive- and negative-parity sides of the cluster that is more pronounced than in the case of microlensing. For example, on the negative-parity side, subhalos with cores larger than about 50 pc do not generate any images with magnification above ∼100 outside of the immediate vicinity of the cluster critical curve. We discuss these factors using analytical and numerical analysis, and exploit them to identify observable signatures of subhalos: Subhalos create pixel-to-pixel flux variations of ≳0.1 mag on the positive-parity side of clusters. These pixels tend to cluster around (otherwise invisible) subhalos. Unlike in the case of microlensing, signatures of subhalo lensing can be found up to 1″ away from the critical curves of massive clusters. 

Abstract SN H0pe is a triply imaged supernova (SN) at redshiftz= 1.78 discovered using the James Webb Space Telescope. In order to classify the SN spectroscopically and measure the relative time delays of its three images (designated A, B, and C), we acquired NIRSpec follow-up spectroscopy spanning 0.6–5μm. From the high signal-to-noise spectra of the two bright images B and C, we first classify the SN, whose spectra most closely match those of SN 1994D and SN 2013dy, as a Type Ia SN. We identify prominent blueshifted absorption features corresponding to Siiiλ6355 and CaiiHλ3970 and Kλ3935. We next measure the absolute phases of the three images from our spectra, which allow us to constrain their relative time delays. The absolute phases of the three images, determined by fitting the three spectra to Hsiao07 SN templates, are ${6.5}_{-1.8}^{+2.4}$days, ${24.3}_{-3.9}^{+3.9}$days, and ${50.6}_{-15.3}^{+16.1}$days for the brightest to faintest images. These correspond to relative time delays between Image A and Image B and between Image B and Image C of $-{122.3}_{-43.8}^{+43.7}$days and ${49.3}_{-14.7}^{+12.2}$days, respectively. The SALT3-NIR model yields phases and time delays consistent with these values. After unblinding, we additionally explored the effect of using Hsiao07 template spectra for simulations through 80 days instead of 60 days past maximum, and found a small (11.5 and 1.0 days, respectively) yet statistically insignificant (∼0.25σand ∼0.1σ) effect on the inferred image delays. 

Abstract Supernova (SN) SN H0pe is a gravitationally lensed, triply imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed multiply imaged SNe provide a rare opportunity to constrain the Hubble constant (H₀), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located atz= 1.783 and is the first SN Ia with sufficient light-curve sampling and long enough time delays for anH₀inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry, we measure time delays of Δt_ab= $-{116.6}_{-9.3}^{+10.8}$observer-frame days and Δt_cb= $-{48.6}_{-4.0}^{+3.6}$observer-frame days relative to the last image to arrive (image 2b; all uncertainties are 1σ), which corresponds to a ∼5.6% uncertainty contribution forH₀assuming 70 km s⁻¹Mpc⁻¹. We also constrain the absolute magnification of each image toμ_a= ${4.3}_{-1.8}^{+1.6}$,μ_b= ${7.6}_{-2.6}^{+3.6}$,μ_c= ${6.4}_{-1.5}^{+1.6}$by comparing the observed peak near-IR magnitude of SN H0pe to the nonlensed population of SNe Ia. 

Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. This finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars. 

Over the past century, supernova (SN) searches have detected multiple supernovae (SNe) in hundreds of individual galaxies. So-called SN siblings discovered in the same galaxy present an opportunity to constrain the dependence of the properties of SNe on those of their host galaxies. To investigate whether there is a connection between sibling SNe in galaxies that have hosted multiple SNe and the properties of galaxies, we have acquired integrated optical spectroscopy of 59 galaxies with multiple core-collapse SNe. Perhaps surprisingly, a strong majority of host galaxy spectra fall within the composite region of the Baldwin–Phillips–Terlevich (BPT) diagram. We find a statistically significant difference (Kolmogorov–Smirnov test p-value = 0.044) between the distributions of the [Nii]λ6583/Hα of galaxies that have hosted a majority of SNe Ibc and those that have hosted a majority of Type II supernovae (SNe II), where the majority of Type Ibc supernovae (SNe Ibc) galaxies have, on average, higher ratios. The difference between the distributions of [Nii]λ6583/Hα may arise from either increased contribution from active galactic nuclei or low-ionization nuclear emission-line regions in SNe Ibc host galaxies, greater metallicity for SNe Ibc host galaxies, or both. When comparing the inferred oxygen abundance and the ionization parameter for the galaxies in the star-forming region on the BPT diagram, we find statistically significant differences between the distributions for SNe Ibc hosts and SNe II hosts (p= 0.008 and p= 0.001, respectively), as well as SNe Ib hosts and SNe II hosts (p = 0.030 and p= 0.006, respectively). We also compare the Hα equivalent width distributions, also integrated across the galaxies, and find no significant difference. 

Recent observations of caustic-crossing galaxies at redshift 0.7 ≲ z ≲ 1 show a wealth of transient events. Most of them are believed to be microlensing events of highly magnified stars. Earlier work predicts such events should be common near the critical curves (CCs) of galaxy clusters (“near region”), but some are found relatively far away from these CCs (“far region”). We consider the possibility that substructure on milliarcsecond scales (few parsecs in the lens plane) is boosting the microlensing signal in the far region. We study the combined magnification from the macrolens, millilenses, and microlenses (“3M lensing”), when the macromodel magnification is relatively low (common in the far region). After considering realistic populations of millilenses and microlenses, we conclude that the enhanced microlensing rate around millilenses is not sufficient to explain the high fraction of observed events in the far region. Instead, we find that the shape of the luminosity function (LF) of the lensed stars combined with the amount of substructure in the lens plane determines the number of microlensing events found near and far from the CC. By measuringβ(the exponent of the adopted power law LF,dN/dL = ϕ(L)∝(1/L)^β), and the number density of microlensing events at each location, one can create a pseudoimage of the underlying distribution of mass on small scales. We identify two regimes: (i) positive-imaging regime whereβ > 2 and the number density of events is greater around substructures, and (ii) negative-imaging regime whereβ < 2 and the number density of microlensing events is reduced around substructures. This technique opens a new window to map the distribution of dark-matter substructure down to ∼10³ M_⊙. We study the particular case of seven microlensing events found in the Flashlights program in the Dragon arc (z = 0.725). A population of supergiant stars having a steep LF withβ = 2.55_−0.56^+0.72fits the distribution of these events in the far and near regions. We also find that the new microlensing events from JWST observations in this arc imply a surface mass density substructure of Σ_∗= 54M_⊙pc⁻², consistent with the expected population of stars from the intracluster medium. We identify a small region of high density of microlensing events, and interpret it as evidence of a possible invisible substructure, for which we derive a mass of ∼1.3 × 10⁸ M_⊙(within its Einstein radius) in the galaxy cluster.