Galaxy Formation and Reionization: Key Unknowns and Expected Breakthroughs by the James Webb Space Telescope

The launch of the James Webb Space Telescope (JWST) in late 2021 marks a new start for studies of galaxy formation at high redshift (z greater than or similar to 6) during the era of cosmic reionization. JWST can capture sensitive, high-resolution images and multiobject spectroscopy in the IR that will transform our view of galaxy formation during the first billion years of cosmic history. This review summarizes our current knowledge of the role of galaxies in reionizing intergalactic hydrogen ahead of JWST, achieved through observations with the Hubble Space Telescope and ground-based facilities including Keck, the Very Large Telescope, Subaru, and the Atacama Large Millimeter/Submillimeter Array. We identify outstanding questions in the field that JWST can address during its mission lifetime, including with the planned JWST Cycle 1 programs. These findings include the following: Surveys with JWST have sufficient sensitivity and area to complete the census of galaxy formation at the current redshift frontier (z similar to 8-10). Rest-frame optical spectroscopy with JWST of galaxies will newly enable measures of star-formation rate, metallicity, and ionization at z similar to 8-9, allowing for the astrophysics of early galaxies to be constrained. The presence of evolved stellar populations at z similar to 8-10 can be definitively tested by JWST, which would provide evidence of star formation out to z similar to 15.

Automated summary

The launch of the James Webb Space Telescope (JWST) in late 2021 provides new opportunities for studying galaxy formation during the cosmic reionization era. JWST's capabilities in capturing high-resolution images and conducting spectroscopy in the IR will significantly enhance our understanding of early galaxy formation. This review summarizes the current knowledge in this field achieved through observations with the Hubble Space Telescope and ground-based facilities, and identifies outstanding questions that can be addressed by JWST.