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

Brenda Frye, Massimo Pascale+40 more|arXiv (Cornell University)|Sep 13, 2023

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper presents the James Webb Space Telescope (JWST) discovery of a multiply-imaged Type Ia supernova, SN H0pe, at z = 1.78, lensed by the galaxy cluster PLCK G165.7+67.0 (z = 0.35), with three distinct images enabling time-delay cosmography. The study constructs a high-precision lens model yielding a total cluster mass of (2.6 ± 0.3) × 10¹⁴ M⊙ and identifies a compact, star-forming galaxy group around the SN host, providing a new path to measure Hubble’s constant H₀ via strong lensing time delays.

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 ($2.6 \pm 0.3) imes 10^{14}$ $M_{\odot}$. 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 $(5.0 \pm 0.1) imes 10^{11}$ $M_{\odot}$. The group members have specific star-formation rates of 2-260 Gyr$^{-1}$ derived from the H$α$-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.

Motivation & Objective

• To measure Hubble’s constant H₀ using time delays from a multiply-imaged Type Ia supernova.
• To characterize the lensing cluster PLCK G165.7+67.0 and its mass distribution via strong gravitational lensing.
• To study the host environment of SN H0pe, including its compact galaxy group and star formation properties.
• To assess the transient potential of the field for future supernova discoveries.
• To validate the use of JWST data for high-precision time-delay cosmography.

Proposed method

• JWST Near Infrared Camera (NIRCam) imaging captured the multiply-imaged supernova SN H0pe in the lensing cluster G165.
• Near-Infrared Spectrograph (NIRSpec) observations confirmed redshifts and kinematics of 11 cluster members, including six in the SN host group.
• A new strong lensing model was constructed using multiple image positions and redshifts, yielding a total cluster mass of (2.6 ± 0.3) × 10¹⁴ M⊙ within 600 kpc.
• Photometry and light curve analysis across nine epochs enabled photometric time delay estimation for SN H0pe.
• Star formation rates (SFRs) were derived from Hα fluxes corrected for dust extinction, stellar absorption, and slit losses.
• The lens model was combined with photometric and spectroscopic time delay estimates to constrain H₀ in a forthcoming analysis (Pascale et al. 2023).

Experimental results

Research questions

• RQ1 Can time delays from a multiply-imaged Type Ia supernova in a strong lensing cluster be used to measure Hubble’s constant H₀?
• RQ2 What is the mass distribution of the galaxy cluster PLCK G165.7+67.0 as constrained by multiple image systems?
• RQ3 What are the physical properties and star formation characteristics of the compact galaxy group hosting SN H0pe?
• RQ4 How does the high star formation rate in the cluster environment affect the likelihood of discovering additional transients?
• RQ5 What is the spectroscopic confirmation status and classification of SN H0pe as a Type Ia supernova?

Key findings

• SN H0pe is a Type Ia supernova at redshift z = 1.78, observed in three distinct positions due to strong gravitational lensing by the cluster G165 (z = 0.35).
• The cluster's total mass within 600 kpc is measured as (2.6 ± 0.3) × 10¹⁴ M⊙ using a new lens model based on 21 image multiplicities and 5 confirmed images.
• A compact galaxy group centered on the SN host galaxy spans a projected extent of ≲33 kpc and has a stellar mass of (5.0 ± 0.1) × 10¹¹ M⊙.
• The group members exhibit specific star-formation rates of 2–260 Gyr⁻¹, indicating ongoing or recent star formation, with the host galaxy possibly transitioning from active to quiescent phases.
• A second, more distant galaxy group at z = 2.24 has a total SFR of ≳100 M⊙ yr⁻¹, implying a supernova rate of ∼1 SNe yr⁻¹, suggesting high transient potential in the field.
• The NIRSpec spectroscopy confirms the SN as a Type Ia and will be used to measure the spectroscopic time delay in a follow-up study (Chen et al. 2023).