Observations of the First Galaxies in the Era of JWST

TL;DR

This review summarizes recent advances in understanding galaxies during the first billion years of cosmic history, highlighting JWST's role in new observations, measurements, and insights into early galaxy properties and reionization.

Contribution

It provides a comprehensive overview of the latest observational methods, measurements, and implications for early galaxies enabled by JWST, including physical properties and reionization contributions.

Findings

New measurements of high redshift galaxy populations

Insights into early galaxy sizes, masses, and metallicities

Constraints on galaxy contributions to reionization

Abstract

We provide a review of our current knowledge of galaxies throughout the first billion years of cosmic history. This field has undergone a transformation in the last two years following the launch of $\textit{JWST}$, and we aim to deliver an observational overview of what we have learned about $z\gtrsim 5$ galaxies. We introduce the latest selection methods of high redshift galaxies and describe new measurements of the census of continuum-selected and dusty star forming galaxies at $z\gtrsim 5$. We discuss new measurements of the UV luminosity function at $z\gtrsim 10$ and associated implications for early star formation. We then summarize what is being learned about the physical properties of early galaxies, with up-to-date discussions of the sizes, masses, ages, metallicities, abundance patterns, UV colors, dust properties, and ionizing sources in $z\gtrsim 5$ galaxies. We review observational evidence for bursty star formation histories and describe prospects for characterizing the duty cycle with future observations. We provide a brief overview of the insight being gained through new detections of AGN in early galaxies. Finally we introduce the latest constraints on the contribution of galaxies to reionziation and discuss how $\textit{JWST}$ measurements of Ly$\alpha$ emission offer the potential to probe the earliest stages of the process. This review is meant to provide a broad introduction to those new to the observational study of very high redshift galaxies.