Accounting for Cosmic Variance in Studies of Gravitationally-Lensed High-Redshift Galaxies in the Hubble Frontier Field Clusters

TL;DR

This paper highlights how gravitational lensing by galaxy clusters increases cosmic variance uncertainty in high-redshift galaxy studies, impacting the accuracy of luminosity functions and star formation rate estimates.

Contribution

It quantifies the increase in cosmic variance uncertainty due to lensing in the Hubble Frontier Fields, emphasizing its importance for interpreting high-redshift galaxy data.

Findings

Cosmic variance uncertainty rises from ~35% at z~7 to >65% at z~10.

Lensing reduces survey volume, increasing variance in galaxy counts.

Previous studies underestimated the impact of cosmic variance on their results.

Abstract

Strong gravitational lensing provides a powerful means for studying faint galaxies in the distant universe. By magnifying the apparent brightness of background sources, massive clusters enable the detection of galaxies fainter than the usual sensitivity limit for blank fields. However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this {\it Letter}, we demonstrate there is an associated increase in the cosmic variance uncertainty. As an example, we show that the cosmic variance uncertainty of the high redshift population viewed through the Hubble Space Telescope Frontier Field cluster Abell 2744 increases from ~35% at redshift z~7 to >~65% at z~10. Previous studies of high redshift galaxies identified in the Frontier Fields have underestimated the cosmic variance uncertainty that will affect the ultimate constraints on both the faint end slope of the high-redshift luminosity function and the cosmic star formation rate density, key goals of the Frontier Field program.