HST Strong-lensing Model for the First JWST Galaxy Cluster SMACS J0723.3−7327

Abstract

On 2022 July 8, NASA shared (https://www.nasa.gov/feature/goddard/2022/nasa-shares-list-of-cosmic-targets-for-webb-telescope-s-first-images) the list of five public showcase targets that have been observed with the new James Webb Space Telescope (JWST) and whose data—at the time of writing—are expected to be released to the public around Tuesday, July 12. One of these targets is the galaxy cluster SMACS J0723.3−7327 (z = 0.39), which acts as a gravitational lens and was recently imaged with the Hubble Space Telescope (HST) in the framework of the Reionization Lensing Cluster Survey (RELICS). To facilitate studies by the community with the upcoming JWST data, we publish here a strong-lensing model for SMACS J0723.3−7327—including mass density and magnification maps. We identify five multiple-image families in the HST imaging. For three of them, system membership and redshift are secured by public spectroscopic data. For the remaining two systems, we rely on robust photometric redshift estimates. We use the Light-Traces-Mass lens modeling method, which complements the parametric models already available in the RELICS repository and elsewhere and thus helps span a representative range of solutions. The new model published here can be accessed on the RELICS website at MAST. It will be interesting to examine which properties of the mass models change and improve, and by how much, when the JWST data are incorporated.