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Supernova (SN) H0pe was discovered as a new transient in James Webb Space Telescope (JWST) NIRCam images of the galaxy cluster PLCK G165.7+67.0 taken as part of the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) JWST GTO program (ID 1176) on 2023 March 30. The transient is a compact source associated with a background galaxy that is stretched and triply imaged by the strong gravitational lensing of the cluster. This paper reports spectra in the 950- 1370 nm observer frame of two of the galaxy images obtained with Large Binocular Telescope (LBT) Utility Camera in the Infrared (LUCI) in long-slit mode two weeks after the JWST observations. The individual and average spectra show the [O′ ¯II] λλ3727,3730 doublet and the Balmer and 4000 Åbreaks at redshift z = 1.783 ± 0.002. The code investigating galaxy emission (CIGALE) best-fit model of the spectral energy distribution indicates that the host galaxy of SN H0pe is massive (Mstar ≃ 6 × 1010 M⊙ after correcting for a magnification factor μ ~ 7) with a predominantly intermediate-age (~2 Gyr) stellar population, moderate extinction, and a magnification-corrected star formation rate ≃13 M⊙ yr-1, consistent with being below the main sequence of star formation. These properties suggest that H0pe might be a type Ia SN. Additional observations of SN H0pe and its host recently carried out with JWST (JWST-DD-4446; PI: B. Frye) will be able to both determine the SN classification and confirm its association with the galaxy analyzed in this work.

The first James Webb Space Telescope (JWST) data on the massive colliding cluster El Gordo allow for 23 known families of multiply lensed images to be confirmed and for eight new members of these families to be identified. Based on these families, which have been confirmed spectroscopically by MUSE, we derived an initial lens model. This model guided the identification of 37 additional families of multiply lensed galaxies, among which 28 are entirely new systems, and nine were previously known. The initial lens model determined geometric redshifts for the 37 new systems. The geometric redshifts agree reasonably well with spectroscopic or photometric redshifts when those are available. The geometric redshifts enable two additional models that include all 60 families of multiply lensed galaxies spanning a redshift range 2 < z < 6. The derived dark-matter distribution confirms the double-peak configuration of mass found by earlier work with the southern and northern clumps having similar masses. We confirm that El Gordo is the most massive known cluster at z > 0.8 and has an estimated virial mass close the maximum mass allowed by standard cosmological models. The JWST images also reveal the presence of small-mass perturbers that produce small lensing distortions. The smallest of these is consistent with being a dwarf galaxy at z = 0.87 and has an estimated mass of 3.8× 109 Mamiddot;, making it the smallest substructure found at z > 0.5. The JWST images also show several candidate caustic-crossing events. One of them is detected at high significance at the expected position of the critical curve and is likely a red supergiant star at z = 2.1878. This would be the first red supergiant found at cosmological distances. The cluster lensing should magnify background objects at z > 6, making more of them visible than in blank fields of a similar size, but there appears to be a deficiency of such objects.

We present a new measurement of the gas-phase mass-metallicity relation (MZR) and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-infrared Deep Extragalactic Survey and the WFC3 Infrared Spectroscopic Parallel Survey. This sample is four times larger than previous metallicity surveys at z ~ 2 and reaches an order of magnitude lower in stellar mass (108 M o?). Using stacked spectra, we find that the MZR evolves by 0.3 dex relative to z ~ 0.1. Additionally, we identify a subset of 49 galaxies with high signal-to-noise (S/N) spectra and redshifts between 1.3 < z < 1.5, where Ha emission is observed along with [O iii] and [O ii]. With accurate measurements of SFR in these objects, we confirm the existence of a mass-metallicity-SFR (M-Z-SFR) relation at high redshifts. These galaxies show systematic differences from the local M-Z-SFR relation, which vary depending on the adopted measurement of the local relation. However, it remains difficult to ascertain whether these differences could be due to redshift evolution, as the local M-Z-SFR relation is poorly constrained at the masses and SFRs of our sample. Lastly, we reproduced our sample selection in the IllustrisTNG hydrodynamical simulation, demonstrating that our line flux limit lowers the normalization of the simulated MZR by 0.2 dex. We show that the M-Z-SFR relation in IllustrisTNG has an SFR dependence that is too steep by a factor of around 3.

Studying the formation and evolution of galaxies at the earliest cosmictimes, and their role in reionization, requires the deepest imaging possible.Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB$\,\sim\,$30,revealing galaxies at the faint end of the LF to $z$$\,\sim\,$9$\,-\,$11 andconstraining their role in reionization. However, a key limitation of thesefields is their size, only a few arcminutes (less than a Mpc at theseredshifts), too small to probe large-scale environments or clusteringproperties of these galaxies, crucial for advancing our understanding ofreionization. Achieving HUDF-quality depth over areas $\sim$100 times largerbecomes possible with a mission like the Wide Field Infrared Survey Telescope(WFIRST), a 2.4-m telescope with similar optical properties to HST, with afield of view of $\sim$1000 arcmin$^2$, $\sim$100$\times$ the area of theHST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering$\sim$100$\,-\,$300$\times$ the area of the HUDF, or up to $\sim$1 deg$^2$, to\mAB$\,\sim\,$30, potentially revealing thousands of galaxies and AGN at thefaint end of the LF, at or beyond $z$\,$\sim$\,9$\,-\,$10 in the epoch ofreionization, and tracing their LSS environments, dramatically increasing thediscovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted asinput to the Astro2020 Decadal Survey, with this version including an Appendix(which exceeded the Astro2020 page limits), describing how the science driversfor a WFIRST Ultra Deep Field might map into a notional observing program,including the filters used and exposure times needed to achieve these depths.)

Studying the formation and evolution of galaxies at the earliest cosmictimes, and their role in reionization, requires the deepest imaging possible.Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB$\,\sim\,$30,revealing galaxies at the faint end of the LF to $z$$\,\sim\,$9$\,-\,$11 andconstraining their role in reionization. However, a key limitation of thesefields is their size, only a few arcminutes (less than a Mpc at theseredshifts), too small to probe large-scale environments or clusteringproperties of these galaxies, crucial for advancing our understanding ofreionization. Achieving HUDF-quality depth over areas $\sim$100 times largerbecomes possible with a mission like the Wide Field Infrared Survey Telescope(WFIRST), a 2.4-m telescope with similar optical properties to HST, with afield of view of $\sim$1000 arcmin$^2$, $\sim$100$\times$ the area of theHST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering$\sim$100$\,-\,$300$\times$ the area of the HUDF, or up to $\sim$1 deg$^2$, to\mAB$\,\sim\,$30, potentially revealing thousands of galaxies and AGN at thefaint end of the LF, at or beyond $z$\,$\sim$\,9$\,-\,$10 in the epoch ofreionization, and tracing their LSS environments, dramatically increasing thediscovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted asinput to the Astro2020 Decadal Survey, with this version including an Appendix(which exceeded the Astro2020 page limits), describing how the science driversfor a WFIRST Ultra Deep Field might map into a notional observing program,including the filters used and exposure times needed to achieve these depths.)