Ly{\alpha} emitters in a cosmological volume I: the impact of radiative transfer

TL;DR

This paper develops a physically-motivated model incorporating radiative transfer effects to predict Lyα emitters in cosmological simulations, improving agreement with observations and highlighting the importance of radiative transfer in galaxy population studies.

Contribution

The authors introduce a novel scheme combining Monte Carlo radiative transfer with fitting formulae to efficiently predict LAEs in large cosmological simulations, accounting for outflow geometries.

Findings

Radiative transfer effects influence LAE host halo mass predictions.

Full models better match observed LAE properties than simple abundance matching.

Incorporating radiative transfer improves the interpretation of LAE clustering data.

Abstract

Lyman-{\alpha} emitters (LAEs) are a promising target to probe the large scale structure of the Universe at high redshifts, $z\gtrsim 2$. However, their detection is sensitive to radiative transfer effects that depend on local astrophysical conditions. Thus, modeling the bulk properties of this galaxy population remains challenging for theoretical models. Here we develop a physically-motivated scheme to predict LAEs in cosmological simulations. The escape of Ly{\alpha} photons is computed using a Monte Carlo radiative transfer code which outputs a Ly{\alpha} escape fraction. To speed-up the process of assigning escape fractions to individual galaxies, we employ fitting formulae that approximate the full Monte Carlo results within an accuracy of 10% for a broad range of column densities, gas metallicities and gas bulk velocities. We apply our methodology to the semi-analytical model GALFORM on a large N-body simulation. The Ly{\alpha} photons escape through an outflowing neutral gas medium, implemented assuming different geometries. This results in different predictions for the typical column density and outflow velocities of the LAE population. To understand the impact of radiative transfer on our predictions, we contrast our models against a simple abundance matching assignment. Our full models populate LAEs in less massive haloes than what is obtained with abundance matching. Overall, radiative transfer effects result in better agreement when confronting the properties of LAEs against observational measurements. This suggest that incorporating the effects of Ly{\alpha} radiative transfer in the analysis of this galaxy population, including their clustering, can be important for obtaining an unbiased interpretation of future datasets.