SKYSURF-3: Testing Crowded Object Catalogs in the Hubble eXtreme Deep Field Mosaics to Study Sample Incompleteness from an Extragalactic Background Light Perspective

TL;DR

This study investigates whether missed faint galaxies in deep Hubble surveys significantly contribute to the discrepancy in extragalactic background light measurements, finding that incompleteness alone cannot fully explain the discrepancy.

Contribution

It simulates higher galaxy densities to quantify survey incompleteness and assesses its impact on EBL measurements, providing new insights into survey limitations.

Findings

Up to 50% of faint galaxies were missed or blended in certain filters.

Incompleteness alone does not account for the entire EBL discrepancy.

Simulations suggest other factors contribute to the EBL measurement gap.

Abstract

Extragalactic Background Light (EBL) studies have revealed a significant discrepancy between direct measurements -- via instruments measuring "bare" sky from which Zodiacal and Galactic light models are subtracted -- and measurements of the Integrated Galaxy Light (IGL). This discrepancy could lie in either method, whether it be an incomplete Zodiacal model or missed faint galaxies in the IGL calculations. It has been proposed that the discrepancy is due to deep galaxy surveys, such as those with the Hubble Space Telescope (HST), missing up to half of the faint galaxies with $24 \le m_{AB} \le 29$ mag. We address this possibility by simulating higher number densities of galaxies, and so assess incompleteness due to object overlap, with three replications of the Hubble UltraDeep Field (HUDF). SourceExtractor is used to compare the recovered counts and photometry to the original HUDF, allowing us to assess how many galaxies may have been missed due to confusion, i.e., due to blending with neighboring faint galaxies. This exercise reveals that, while up to 50% of faint galaxies with $28 \le m_{AB} \le 29$ mag were missed or blended with neighboring objects in certain filters, not enough were missed to account for the EBL discrepancy alone in any of the replications.