Astro2020 Science White Paper: Synergies Between Galaxy Surveys and Reionization Measurements

Understand

The early phases of galaxy formation constitute one of the most exciting frontiers in astrophysics.

• It is during this era that the first luminous sources reionize the intergalactic medium - the moment when structure formation affects every baryon in the Universe.
• Here we argue that we will obtain a complete picture of this era by combining observations of galaxies with direct measurements of the reionization process: the former will provide a detailed understanding of bright sources, while the latter will constrain the (substantial) faint source population.
• We further describe how optimizing the comparison of these two measurements requires near-infrared galaxy surveys covering large volumes and retaining redshift information and also improvements in 21-cm analysis, moving those experiments into the imaging regime.