Dark-ages reionization and galaxy formation simulation – IV. UV luminosity functions of high-redshift galaxies

Abstract

In this paper we present calculations of the UV luminosity function from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAG-ONS) project, which combines N-body, semi-analytic and semi-numerical modelling designed to study galaxy formation during the Epoch of Reionization. Using galaxy formation physics including supernova feedback, the model naturally reproduces the UV LFs for high-redshift star-forming galaxies from z∼5 through to z∼10. We investigate the luminosity-star formation rate (SFR) relation, finding that variable SFR histories of galaxies result in a scatter around the median relation of 0.1-0.3 dex depending on UV luminosity. We find close agreement between the model and observationally derived SFR functions. We use our calculated luminosities to investigate the luminosity function below current detection limits, and the ionizing photon budget for reionization. We predict that the slope of the UV LF remains steep below current detection limits and becomes flat at M UV −14. We find that 48 (17) per cent of the total UV flux at z∼6 (10) has been detected above an observational limit of M UV ∼−17, and that galaxies fainter than M UV ∼−17 are the main source of ionizing photons for reionization. We investigate the luminosity-stellar mass relation, and find a correlation for galaxies with M UV <−14 that has the form M * ∝10 −0.47MUV , in good agreement with observations, but which flattens for fainter galaxies. We determine the luminosity-halo mass relation to be M vir ∝10 −0.35MUV , finding that galaxies with M UV =−20 reside in host dark matter haloes of 10 11.0±0.1 M at z∼6, and that this mass decreases towards high redshift.

The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties

“…In particular, we find that our observational constraints allow for the existence of a flattening or turn-over in the z 6 LF at 15 mag >-as predicted in the theoretical models, due to a variety of physical processes, including a greater role for radiative feedback (O'Shea et al 2015;Ocvirk et al 2016;Yue et al 2016) and less efficient cooling in lower mass halos where atomic cooling processes would be less important Gnedin 2016;Liu et al 2016). The present results suggest that these physical processes can impact the shape of the LF at 15 mag >-, as is predicted, and there is no fundamental disagreement with observational results to 14 mag >-(contrary to reports from L17).…”

“…The semi-numerical models include gas cooling physics, star-formation prescriptions, feedback, and merging prescriptions, among other components of the model. The turn-over in the LF results of Liu et al (2016) at approximately−12 mag correspond to the approximate halo masses ∼10…”

“…DRAGONS (Liu et al 2016): the LF results from Liu et al (2016) are based on the Dark-ages Reionization And Galaxyformation Observables from Numerical Simulations (DRA-GONS) 18 project, which builds semi-numerical models of galaxy formation on top of halo trees derived from N-body simulations done over different box sizes to probe a large dynamical range. The semi-numerical models include gas cooling physics, star-formation prescriptions, feedback, and merging prescriptions, among other components of the model.…”

“…8 In addition to the clear scientific importance of the faint-end slope α for computing the total ionizing emissivity from faint galaxies, the observations also allow us to test for a possible flattening or turn-over of the UV LF at low luminosities. Many cosmological hydrodynamic simulations of galaxy formation predict a flattening in the UV LF at approximately−13 or approximately−15magdue to less efficient atomic and molecular hydrogen cooling, respectively (Muñoz & Loeb 2011;Krumholz & Dekel 2012;Jaacks et al 2013;Kuhlen et al 2013;Wise et al 2014;Finlator et al 2016;Gnedin 2016;Liu et al 2016), while other simulations predict a flattening in the rangeapproximately−16 to approximately−13 magdue to the impact of radiative feedback (O'Shea et al 2015;Ocvirk et al 2016). Meanwhile, by combining abundance matching and detailed studies of the color-magnitude diagram of lowluminosity dwarfs in the local universe, evidence for a lowmass turn-over in the LF has been reported at −13 mag (Boylan-Kolchin et al 2015 see also Boylan-Kolchin et al 2014).…”

Dark-ages reionization and galaxy formation simulation – X. The small contribution of quasars to reionization

“…19 Dust attenuation is not considered because these relatively faint galaxies have little dust in our models (Liu et al 2016). .…”