A Shining Cosmic Dawn: Constraining Luminosity Functions and the Clustering of Luminous Galaxies at z > 8 with the Roman High-Latitude Wide-Area Survey

A Shining Cosmic Dawn: Constraining Luminosity Functions and the Clustering of Luminous Galaxies at z > 8 with the Roman High-Latitude Wide-Area Survey

Program ID	19100
Science Category	Galaxies
Program Type	Analysis
Category	Medium
Principal Investigator	Jakob Helton
PI Institution	Pennsylvania State University
Co-Investigators	William Baker (Niels Bohr Institute, University of Copenhagen) Nikko Cleri (Pennsylvania State University) Qiao Duan (University of Cambridge) Daniel Eisenstein (Harvard University) Kevin Hainline (University of Arizona) Joel Leja (Pennsylvania State University) Pierluigi Rinaldi (Space Telescope Science Institute / STScI) Sandro Tacchella (University of Cambridge) Lily Whitler (University of Cambridge) Christopher Willmer (University of Arizona) Zihao Wu (Harvard University)
Abstract	JWST has discovered a substantial population of luminous galaxies in the first few hundred million years after the Big Bang, revealing an early Universe that was far more mature than expected. These results have sparked a fierce debate about whether our understanding of the primordial Universe needs revision. However, JWST's limited field-of-view has made it difficult to build statistical samples of galaxies at z > 8 across wide areas of the sky. These samples are necessary for minimizing the effects of cosmic variance while constraining the bright end of ultraviolet luminosity functions and measuring two-point correlation functions. We propose to analyze observations from the deep tier of Roman's High-Latitude Wide-Area Survey (HLWAS) to study the abundance and clustering of the most distant galaxies by constructing the largest sample of luminous galaxy candidates ever assembled at z > 8. Compared to existing programs from HST and JWST, the deep tier of the HLWAS provides at least an order of magnitude increase in survey area at similar depths. This proposal will find record-breaking galaxies in the first 300 million years of cosmic history, allowing us to distinguish between competing theoretical predictions, since they diverge most strongly for the brightest and rarest objects. Our sample of galaxies can be spectroscopically confirmed with JWST in relatively short exposure times, which allows for efficient, targeted follow-up observations that maximize the scientific return of both JWST and Roman. The proposed work represents an important step toward one of Roman's primary mission goals: understanding how different types of galaxies form, grow, interact with their environments, and evolve with time.