The UV colours and dust attenuation of Lyman-break galaxies

TL;DR

This study uses a semi-analytical galaxy formation model to analyze the UV colours and dust effects on Lyman-break galaxies across high redshifts, highlighting the importance of dust properties in interpreting observations.

Contribution

It provides a self-consistent model of dust attenuation affecting UV colours of LBGs, evaluating the effectiveness of the drop-out selection technique and the impact of dust extinction curves.

Findings

Brighter galaxies experience stronger dust attenuation.

Drop-out technique effectively selects over 70% of UV bright galaxies.

UV colours are highly sensitive to dust extinction curve assumptions.

Abstract

Using GALFORM, a semi-analytical model of galaxy formation in the Lambda cold dark matter cosmology, we study the rest-frame ultraviolet (UV) colours of Lyman-break galaxies (LBGs) in the redshift range 2.5 < z < 10. As the impact of dust on UV luminosity can be dramatic, our model includes a self-consistent computation of dust attenuation based on a radiative transfer model. We find that intrinsically brighter galaxies suffer stronger dust attenuation than fainter ones, though the relation has a large scatter. The model predicts galaxies with UV colours consistent with the colour selection regions designed to select LBGs in observational surveys. We find that the drop-out technique that selects LBGs based on two rest-frame UV colours is robust and effective, selecting more than 70 per cent of UV bright galaxies at a given redshift. We investigate the impact on the predicted UV colours of varying selected model parameters. We find that the UV colours are most sensitive to the modelling of dust attenuation and in particular, to the extinction curve used in the radiative transfer calculation. If we assume a Milky Way dust extinction curve, the predicted UV continuum slopes are, in general, bluer than observed. However, we find that the opposite is true when using the Small Magellanic Cloud dust extinction curve. This demonstrates the strong dependence of UV colours on dust properties and highlights the inadequacy of using the UV continuum slope as a tracer of dust attenuation without any further knowledge of the galaxy inclination or dust characteristics in high redshift galaxies.