The first science image released by the James Webb Space Telescope (JWST) was of a gravitational lens, in particular the galaxy cluster SMACS J0723.3-7327. Gravitational lenses, especially galaxy clusters, magnify the light from background galaxies and produce multiple images of these. Before JWST, 19 multiple images of six background sources were known in SMACS J0723.3-7327. The JWST data now revealed 27 additional multiple images from another ten lensed sources.
"In this first step towards the road opened by JWST, we used recent data from this brand new telescope, to model the lensing effect of SMACS0723 with great accuracy," points out Gabriel Bartosch Caminha, postdoc fellow at TUM, the Max Planck Institute for Astrophysics (MPA) and the German Centre for Cosmological Lensing (GCCL). The collaboration first used data from the Hubble Space Telescope (HST) and Multi Unit Spectroscopic Explorer (MUSE) to build a "pre-JWST" lens model, and then refined it with newly available JWST near-infrared imaging. "The JWST imaging is absolutely astounding and beautiful, showing many more multiply lensed background sources, which allowed us to substantially refine our lens mass model," he adds.
The new model for the mass distribution of the foreground cluster is capable of reproducing the positions of all multiple images with a high accuracy, making the model one of the most accurate available. For follow-up studies of these sources, the lens models, including magnification maps and redshifts (i.e. distances) estimated from the model are made publicly available. "We are very excited about this," Suyu adds, "we are eagerly awaiting future JWST observations of other strong lensing galaxy clusters. These will not only allow us to better constrain the mass distributions of galaxy clusters, but also to study high-redshift galaxies."