The JWST Discovery of the Triply-imaged Type Ia "Supernova H0pe" and Observations of the Galaxy Cluster PLCK G165.7+67.0

Abstract: A Type Ia supernova (SN) at $z=1.78$ was discovered in James Webb Space Telescope Near Infrared Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; $z = 0.35$). The SN is situated 1.5-2 kpc from the host-galaxy nucleus and appears in three different locations as a result of gravitational lensing by G165. These data can yield a value for Hubble's constant using time delays from this multiply-imaged SN Ia that we call "SN H0pe." Over the cluster, we identified 21 image multiplicities, confirmed five of them using the Near-Infrared Spectrograph, and constructed a new lens model that gives a total mass within 600 kpc of ($2.6 \pm 0.3) \times 10^{14}$ $M_{\odot}$. The photometry uncovered a galaxy overdensity coincident with the SN host galaxy. NIRSpec confirmed six member galaxies, four of which surround the SN host galaxy with relative velocity $\lesssim$900 km s$^{-1}$ and projected physical extent $\lesssim$33 kpc. This compact galaxy group is dominated by the SN host galaxy, which has a stellar mass of $(5.0 \pm 0.1) \times 10^{11}$ $M_{\odot}$. The group members have specific star-formation rates of 2-260 Gyr$^{-1}$ derived from the H$\alpha$-line fluxes corrected for stellar absorption, dust extinction, and slit losses. Another group centered on a strongly-lensed dusty star forming galaxy is at $z=2.24$. The total (unobscured and obscured) SFR of this second galaxy group is estimated to be ($\gtrsim$100 $M_{\odot}$ yr$^{-1}$), which translates to a supernova rate of $\sim$1 SNe yr$^{-1}$, suggesting that regular monitoring of this cluster may yield additional SNe.

• The paper presents the discovery of triply-imaged Type Ia Supernova H0pe at redshift 1.78, offering a novel pathway for H₀ determination using gravitational lensing.
• It details the use of JWST NIRCam imaging and a new lensing model based on 21 multiply-imaged systems to map the mass distribution of galaxy cluster PLCK G165.7+67.0.
• The study also examines the host galaxy’s compact group dynamics, providing actionable insights into cluster evolution and galaxy formation at high redshifts.

Overview and Implications of "The JWST Discovery of the Triply-imaged Type Ia 'Supernova H0pe' and Observations of the Galaxy Cluster PLCK G165.7+67.0"

This essay summarizes a comprehensive study involving the discovery of a triply-imaged Type Ia supernova, named "Supernova H0pe," in the galaxy cluster PLCK G165.7+67.0 using the James Webb Space Telescope (JWST). This work, leveraging the Near Infrared Camera (NIRCam) on JWST, reports critical observations with significant implications for cosmology, particularly concerning the measurement of the Hubble constant (H_0) through time-delay cosmography.

Key Findings

1. Discovery and Characteristics of Supernova H0pe: The identification of a Type Ia supernova at a redshift z = 1.78, named "Supernova H0pe," was enabled by the JWST NIRCam imaging of galaxy cluster PLCK G165.7+67.0 (z = 0.35). The supernova was observed in three distinct locations due to gravitational lensing effects by the cluster, an occurrence providing an excellent opportunity to measure time-delay parameters crucial for Hubble constant estimations.
2. Galaxy Cluster Analysis and Lensing Model: The study identified 21 multiply-imaged systems within the galaxy cluster, of which five were corroborated using the Near-Infrared Spectrograph (NIRSpec), creating a new lens model. The mass model estimates a total mass near (2.6 ± 0.3) × 10^14 solar masses within a 600 kpc radius, based on lensing constraints.
3. Supernova Host Galaxy and Compact Group Dynamics: The host galaxy of the supernova was in proximity to a compact group with four spectroscopically confirmed members, each with a relative velocity of less than 900 km/s and separated by less than 33 kpc. The host exhibits a stellar mass of around (5.0 ± 0.1) × 10^11 solar masses, with group members reflecting diverse star-formation rates ranging from 2 to 260 Gyr^-1, indicative of varying degrees of stellar formation activity.
4. Further Observational Insights: The paper adds depth to our understanding of galaxy clusters through the detailed mapping of lensed arcs and the spectroscopic investigation, exploring two distinct galaxy groups at redshifts z = 1.78 and z = 2.24. It reports a significant star-formation rate (SFR) from one subset of galaxies possibly indicating a widespread area of enhanced galaxy formation activity.

Implications for Cosmology and Future Observations

The ability to use a multiply-imaged supernova for time-delay cosmography exemplifies a refined method for improving H_0 accuracy, a critical parameter in understanding the universe's expansion rate. These observations establish a promising basis for using gravitational lensing in conjunction with Type Ia supernovae as precise cosmological probes.

• Cosmological Modeling Advancement: This study shows potential advancements in measuring cosmological distances and constraining dark energy models through the gravitational lensing effect and time-delayed light curves from supernovae. The variability and distribution of image delays across many supernova images within this lensing framework offer new paths to refine H_0 measurements.
• Expansion on Galaxy Evolution Studies: Discoveries related to the compact galaxy groups, their mass distributions, and formation activities can enhance understanding of galaxy cluster evolution. With ongoing data from JWST, there exist significant opportunities to pursue more in-depth examinations into the high-redshift universe and the role of galaxy interactions during cosmic dawn.
• Future JWST Applications: The high sensitivity of JWST and its ability to resolve faint, multiplied images of distant supernovae present future opportunities to observe more such events, extending these methodologies to other galaxy clusters and adding robustness to cosmological studies.

In conclusion, this comprehensive investigation leveraging JWST offers valuable insights into gravitational lensing, galaxy cluster mass dynamics, and cosmology. The techniques demonstrated here, combined with future observations, could significantly sharpen our understanding of universe expansion and galaxy formation across cosmic time.