Photometric Selection of z~5 Lyman Break Galaxies in the ESO Remote Galaxy Survey

TL;DR

This paper presents a photometric method to select z~5 Lyman Break Galaxies using multi-wavelength data, evaluates the sample's reliability, and confirms a lower bright-end UV luminosity function compared to z=4.

Contribution

It introduces a refined photometric selection technique for z~5 LBGs and assesses its reliability and implications for galaxy evolution studies.

Findings

Sample reliability is approximately 60%, improved to 80% with near-infrared criteria.

Over 30% of high-reliability candidates show multiple UV-bright components or disturbed morphology.

The bright-end UV luminosity function at z=5 is lower than at z=4 by a factor of 3, with M*uv=-20.9±0.2.

Abstract

We describe the selection of a sample of photometrically-defined Lyman break galaxies (LBGs) at z~5 using the multi-wavelength imaging data of the ESO Remote Galaxy Survey (ERGS). The data is drawn from ten widely-separated fields covering a total sky area of 275 arcmin squared. Starting with a simple colour (R-I>1.3) and magnitude (I<26.3) cut to isolate the Lyman break and then refining the sample by applying further optical and near-infrared photometric criteria we identify a sample of 253 LBG candidates. We carefully model the completeness of this sample and the factors that affect its reliability. There is considerable overlap between this sample and a spectroscopically-confirmed sample drawn from the same survey and this allows us to determine the reliability of the optical photometric selection (~60 per cent) and to show that the reliability can be significantly improved (to ~80 per cent) by applying near-infrared waveband criteria to exclude very red contaminants. Even this high level of reliability may compromise some statistical studies of LBG properties. We show that over 30 per cent of the highest reliability candidates have multiple UV-luminous components and/or disturbed morphology in HST imaging, though it is unclear whether this represents multiple interacting/merging sources or individual large sources with multiple UV bright regions. Using this sample we confirm that the normalisation of the bright end of the z=5 UV luminosity function (down to M*) is lower than the same at z=4 by a factor of 3. Using a Schechter fit we determine M*uv=-20.9+/-0.2. We discuss whether it is reasonable to expect the UV luminosity function to follow a Schechter function, given the UV emission is short-lived and stochastic, and does not necessarily trace the underlying mass of the galaxy.