The ultraviolet colours and dust attenuation of Lyman-break galaxies

Abstract

Using galform, a semi-analytical model of galaxy formation in the Λ 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.

The star formation and AGN luminosity relation: predictions from a semi-analytical model

“…The model is successful in reproducing many observations, including the luminosity and stellar mass functions of galaxies, the number counts of SMGs, the evolution of Lyα and LBGs, H and H 2 mass functions and the AGN diversity and evolution (Baugh et al 2005;Bower et al 2006;Orsi et al 2008;Fanidakis et al 2011Fanidakis et al , 2012Fanidakis et al , 2013aKim et al 2011;Lacey et al 2011;Lagos et al 2011Lagos et al , 2012Lagos et al , 2014aGonzalez-Perez et al 2013. The model provides a very good fit to the Herschel FIR galaxy LFs and number counts (Lacey et al, in preparation;see also Lacey et al 2010) and X-ray LFs of AGNs in the z = 0-3 universe Fanidakis et al, in preparation) and therefore it is an ideal tool for studying the correlation between SFR and AGN activity.…”

Predicting Hα emission-line galaxy counts for future galaxy redshift surveys

“…Molecular clouds are regarded as the birth places of new stars and sites of ongoing starformation, and so we would therefore expect them to be intense sources of emission lines. As such, it is necessary to either incorporate molecular clouds into the Ferrara et al method (as has been done for instance in the GALFORM semi-analytical model, see for example Cole et al 2000, Gonzalez-Perez et al 2013and Lacey et al 2016. We can introduce nebular dust attenuation using the approach from the Charlot & Fall (2000) method described previously.…”

The 0.1 <z< 1.65 evolution of the bright end of the [O ii] luminosity function

“…In particular, if we take into account that the dust extinction applied to the [O] line is the same as experienced by the continuum at that wavelength, the line could actually be more attenuated than predicted here. The main uncertainty for the Hα line is the dust attenuation (see Gonzalez-Perez et al 2013, for a detailed description of the dust treatment in the models). Figure 16 also shows the [O] LF predicted by the GP14 model imposing a cut in magnitude similar to that done observationally.…”