Finding High-Redshift Galaxies with JWST

TL;DR

This paper discusses how cosmic variance impacts the detection and analysis of early galaxies with JWST, emphasizing the importance of survey design to mitigate uncertainties in high-redshift galaxy counts.

Contribution

It demonstrates that cosmic variance significantly affects high-redshift galaxy observations and evaluates strategies like adding independent pointings to improve survey effectiveness.

Findings

Cosmic variance dominates uncertainty in high-redshift galaxy counts.

Median counts are below average due to galaxy clustering.

Independent pointings improve detection and constraint of galaxy properties.

Abstract

One of the primary goals for the upcoming James Webb Space Telescope (JWST) is to observe the first galaxies. Predictions for planned and proposed surveys have typically focused on average galaxy counts, assuming a random distribution of galaxies across the observed field. The first and most massive galaxies, however, are expected to be tightly clustered, an effect known as cosmic variance. We show that cosmic variance is likely to be the dominant contribution to uncertainty for high-redshift mass and luminosity functions, and that median high-redshift and high-mass galaxy counts for planned observations lie significantly below average counts. Several different strategies are considered for improving our understanding of the first galaxies, including adding depth, area, and independent pointings. Adding independent pointings is shown to be the most efficient both for discovering the single highest-redshift galaxy and also for constraining mass and luminosity functions.