FIRSTLIGHT · Exploring Cosmic Dawn with James Webb Space Telescope

The cosmic dark ages - when the Universe was filled with neutral hydrogen that was opaque to ultraviolet light - are thought to have ended around one billion years after the Big Bang, when first light sources produced enough energetic photons to ionize the neutral hydrogen. This phase is referred to as the epoch of reionization and is also the era of the first galaxies' formation. However, this is also one of the least understood epochs in the Universe's evolution. When did it start/end? Was it patchy or smooth? How did galaxies reionize the Universe (if they did)? What are the properties of the earliest galaxies? To answer these questions, this proposal will use deep observations of the largest sample of the most powerful cosmic telescopes that will be observed with the James Webb Space Telescope (JWST) right after its launch. Compared to all previous facilities, JWST’s capabilities are dazzling. Its instruments will provide data beyond those yet seen by any astronomer. However, with high power comes great responsibility. Given its limited lifetime, excellent leadership needs to be established. As a key member of the Near-Infrared Imager and Slitless Spectrograph (NIRISS) team with guaranteed time and a member of the Early Release Science program, I am in a unique position to guarantee success of this project. I am proposing to relocate to Europe. JWST's NIRISS instrument is not represented in Europe, and this program will bring immediate and proprietary access to the data. This proposal will (1) determine the timeline of reionization, (2) identify the exact role first galaxies played in this process by studying their ionized bubbles, and (3) determine stellar properties of the earliest galaxies. With an unprecedented facility, the program will undoubtedly bring many exciting discoveries and allow the first look at the details of the Cosmic Dawn.