We stand on the verge of completing our cosmic history. With Hubble and Spitzer, we have seen galaxies 97% of the way back to the Big Bang at z ~ 11 (400 Myr). And with JWST, we aim to detect the first galaxies. Gravitational lensing by galaxy clusters has enabled efficient discovery of such distant galaxies, yielding images brightly magnified for more detailed study as well as the intrinsically faintest galaxies yet known (nJy sources). I will review results to date from CLASH, the Frontier Fields, RELICS, and BUFFALO. Future observations with JWST will yield detailed properties of these galaxies and discover evermore distant galaxies at z > 11. At these very early times, the discovery efficiency gains from lensing will be even more pronounced if luminosity function faint end slopes are steeper than alpha ~ -2, as suggested by current models and observational extrapolations. Based on these extrapolations, I predict that gravitational lensing will be the key to discovering the first galaxies with JWST.

Reviewed cluster lensing results to date from CLASH, the Frontier Fields, RELICS, and BUFFALO, and presented predictions for JWST. Workshop "First Galaxies, First Structures" October 21-25 2019 Observatory of Paris.