The first scientific image released by the James Webb Space Telescope (JWST) shows a gravitational lens, namely the galaxy cluster SMACS J0723.3−7327. Gravitational lenses, especially galaxy clusters, magnify the light from background galaxies and produce multiple images of them. Before JWST, a total of 19 multiple images from six background sources were known around SMACS J0723.3−7327. The JWST data now revealed 27 additional multiple images of ten more lensed sources.
Ancient galaxy discovered
The researchers first used data from the Hubble Space Telescope (HST) and the Multi Unit Spectroscopic Explorer (MUSE) to create a 'pre-JWST' lens model, and then refined it with the newly available JWST near-infrared imaging. Many of these new, lensed sources do not yet have distance estimates, and the scientists used their mass model to predict how far away these lensed galaxies are most likely to be. One of them was found to be probably at the astonishing distance of 13 billion light-years (redshift > 7.5), meaning its light was emitted in the early stages of our Universe. This galaxy is multiply lensed into three images and its total luminosity is magnified by a factor of 20.
New mass model for gravitational lenses
However, in order to study such primordial objects, it is essential to accurately describe the lensing effect of the foreground galaxy cluster. "Our accurate mass model forms the foundation for the exploration of JWST data," emphasizes Sherry Suyu, ORIGINS-PI, research group leader at MPA, associate professor at the Technical University of Munich and visiting scientist at the Academia Sinica Institute of Astronomy and Astrophysics. "The spectacular JWST images show a great variety of strongly lensed galaxies, which can now be studied in detail thanks to our accurate model," explains Suyu.
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, outperforming other existing mass models. 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.”
Publication: "First JWST observations of a gravitational lens: Mass model of new multiple images with near-infrared observations of SMACS~J0723.3−7327", G. B. Caminha, S. H. Suyu, A.Mercurio et al, A&A Letters (2022)
Prof. Sherry Suyu
Max-Planck-Institut for Astrophysics / Technical University Munich