On Contamination and Completeness in z>5 Lyman Break Galaxy Surveys

TL;DR

This paper analyzes the challenges of sample completeness and contamination in high-redshift z>5 Lyman break galaxy surveys, highlighting biases and their impact on luminosity functions and clustering measurements.

Contribution

It provides a detailed assessment of contamination sources and selection biases in z>5 galaxy surveys, using spectroscopic data to improve understanding of sample reliability.

Findings

Most surveys underestimate contamination from z=1 galaxies and stars.

Moderate Lyman-alpha emitters are often missed, affecting luminosity estimates.

Contamination and selection biases influence clustering and luminosity function results.

Abstract

A large population of z>5 Lyman break galaxies has been identified in recent years. However, the high redshift galaxies selected by different surveys are subject to a variety of selection effects - some overt, others more subtle. We present an analysis of sample completeness and contamination issues in high redshift surveys, focusing on surveys at z=5 and using a spectroscopically-confirmed low redshift sample from the DEEP2 survey in order to characterise contaminant galaxies. We find that most surveys underestimate their contamination from highly clustered galaxies at z=1 and stars. We consider the consequences of this for both the rest-frame ultraviolet luminosity function and the clustering signal from z=5 galaxies. We also find that sources with moderate strength Lyman-alpha emission lines can be omitted from dropout surveys due to their blue colours, again effecting the derived luminosity functions. We discuss the points of comparison between different samples, and the applicability of survey-specific results to the population at z>5 in general.