James Webb Space Telescope Discovery

A Bright and Shiny Result from PEARLS

We report the discovery of a new transient in James Webb Space Telescope (JWST) NIRCam exposures of the massive galaxy cluster PLCK G165.7+67 (G165) taken as part of the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) program (GTO-1176; PI: R. Windhorst). The source was not detected in previous Hubble Space Telescope images (Frye et al. 2019; Pascale et al. 2022). Follow-up spectroscopy was accomplished using the Large Binocular Telescope (LBT) LUCI in a consortium-wide effort. The partners from Germany allocated the telescope time, the partners from Italy prepared, carried out, and reduced the spectroscopy, and the partners from UArizona directly supported the organization and observing activities. As a result of this grand effort, the redshift of the SN host was measured. Additional imaging and spectroscopy have been carried out with JWST (DD-4446; PI: B. Frye). This one transient is detected in three different locations (a, b, and c) as a result of gravitational lensing by the foreground galaxy cluster G165. Our gravitational lensing model predicts that light from the transient arrived first in image “a,” followed by “c,” and then “b”. This transient, which we designate as "SN H0pe," is s Type Ia supernova that was classified as a result of analyzing the JWST observations. Accepted paper abstract: 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 Å breaks 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 (M_star ≃ 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 paper has been accepted on A&A Journal. Credit: University of Arizona Figure caption: JWST/NIRCam color image in the central region of G165. {\it Right:} Closeup of the boxed region depicting the three images of the galaxy Arc 2, as labeled. The SN Ia candidate is circled. Note the parity flip between images 2c and 2b, and images 2b and 2a, as predicted by lensing theory. The SN Ia candidate appears in all three images. Raw images Article images (unofficial)