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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. 

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. 

Abstract We present a new parametric lens model for the G165.7+67.0 galaxy cluster, which was discovered with Planck through its bright submillimeter flux, originating from a pair of extraordinary dusty star-forming galaxies (DSFGs) atz≈ 2.2. Using JWST and interferometric mm/radio observations, we characterize the intrinsic physical properties of the DSFGs, which are separated by only ∼1″ (8 kpc) and a velocity difference ΔV≲ 600 km s⁻¹in the source plane, and thus are likely undergoing a major merger. Boasting intrinsic star formation rates SFR_IR= 320 ± 70 and 400 ± 80M_⊙yr⁻¹, stellar masses of $\log \left[M_{\star }/M_{\odot }\right]=10.2\pm 0.1$and 10.3 ± 0.1, and dust attenuations ofA_V= 1.5 ± 0.3 and 1.2 ± 0.3, they are remarkably similar objects. We perform spatially resolved pixel-by-pixel spectral energy distribution (SED) fitting using rest-frame near-UV to near-IR imaging from JWST/NIRCam for both galaxies, resolving some stellar structures down to 100 pc scales. Based on their resolved specific star formation rates (SFRs) andUVJcolors, both DSFGs are experiencing significant galaxy-scale star formation events. If they are indeed interacting gravitationally, this strong starburst could be the hallmark of gas that has been disrupted by an initial close passage. In contrast, the host galaxy of SN H0pe has a much lower SFR than the DSFGs, and we present evidence for the onset of inside-out quenching and large column densities of dust even in regions of low specific SFR. Based on the intrinsic SFRs of the DSFGs inferred from UV through far-infrared SED modeling, this pair of objects alone is predicted to yield an observable 1.1 ± 0.2 core-collapse supernovae per year, making this cluster field ripe for continued monitoring. 

ABSTRACT The Reionization Cluster Survey imaged 41 galaxy clusters with the Hubble Space Telescope (HST), in order to detect lensed and high-redshift galaxies. Each cluster was imaged to about 26.5 AB mag in three optical and four near-infrared bands, taken in two distinct visits separated by varying time intervals. We make use of the multiple near-infrared epochs to search for transient sources in the cluster fields, with the primary motivation of building statistics for bright caustic crossing events in gravitational arcs. Over the whole sample, we do not find any significant (≳5σ) caustic crossing events, in line with expectations from semi-analytical calculations but in contrast to what may be naively expected from previous detections of some bright events or from deeper transient surveys that do find high rates of such events. Nevertheless, we find six prominent supernova (SN) candidates over the 41 fields: three of them were previously reported and three are new ones reported here for the first time. Out of the six candidates, four are likely core-collapse SNe – three in cluster galaxies, and among which only one was known before, and one slightly behind the cluster at z ∼ 0.6–0.7. The other two are likely Ia – both of them previously known, one probably in a cluster galaxy and one behind it at z ≃ 2. Our study supplies empirical bounds for the rate of caustic crossing events in galaxy cluster fields to typical HST magnitudes, and lays the groundwork for a future SN rate study. 

Abstract We derive the spatial and wavelength behavior of dust attenuation in the multiple-armed spiral galaxy VV 191b using backlighting by the superimposed elliptical system VV 191a in a pair with an exceptionally favorable geometry for this measurement. Imaging using the James Webb Space Telescope and Hubble Space Telescope spans the wavelength range 0.3–4.5μm with high angular resolution, tracing the dust in detail from 0.6–1.5μm. Distinct dust lanes continue well beyond the bright spiral arms, and trace a complex web, with a very sharp radial cutoff near 1.7 Petrosian radii. We present attenuation profiles and coverage statistics in each band at radii 14–21 kpc. We derive the attenuation law with wavelength; the data both within and between the dust lanes clearly favor a stronger reddening behavior (R=A_V/E_B−V≈ 2.0 between 0.6 and 0.9μm, approaching unity by 1.5μm) than found for starbursts and star-forming regions of galaxies. Power-law extinction behavior ∝λ^−βgivesβ= 2.1 from 0.6–0.9μm.Rdecreases at increasing wavelengths (R≈ 1.1 between 0.9 and 1.5μm), whileβsteepens to 2.5. Mixing regions of different column density flattens the wavelength behavior, so these results suggest a different grain population than in our vicinity. The NIRCam images reveal a lens arc and counterimage from a background galaxy atz≈ 1, spanning 90° azimuthally at 2.″8 from the foreground elliptical-galaxy nucleus, and an additional weakly lensed galaxy. The lens model and imaging data give a mass/light ratioM/L_B= 7.6 in solar units within the Einstein radius 2.0 kpc.