Modelling LAEs in the Epoch of Reionization with OBELISK

Abstract

Lya emitters (LAEs) are particularly useful objects for the study of the Epoch of Reionization. Lya profiles can be used to estimate the amount of ionizing photons that are able to escape the galaxies, and therefore to understand what objects contributed to reionization. However, Lya is a resonant line and its complex radiative transfer effects make the interpretation of the line challenging and require the use of appropriate radiative transfer methods for anything but the simplest gas distributions. With this work we aim to study the properties of simulated LAEs, and the robustness of these inferred properties under a change in the dust model. We also explore the Lyman Continuum (LyC) escape fraction of these galaxies and compare our results with observationally calibrated methods to infer this quantity from the Lya spectrum. We use the radiative transfer code RASCAS to perform synthetic observations of 13 flux-selected galaxies from the Obelisk simulation at redshift z = 6, towards the end of the Epoch of Reionization. Each galaxy was observed in Lya, ionizing and non-ionizing continuum from 48 different viewing angles. We show that the Lya profiles emitted from a galaxy present large variations with a change in viewing angle and that the relation between peak separation and Lya escape fraction is not as strong as previously found, as we find lines of sight with both low peak separation and low escape fraction, due to their dust content. We also show that the properties of the Lya line are reasonably robust under a change in dust model. Lastly, we compare the LyC escape fractions we derive from the simulation to three observationally calibrated methods of inferring this quantity. We determine that none of these relations reproduce the scatter that we find in our sample, and that high escape fraction lines of sight have both low peak separation and low dust extinction in the UV.

Resubmitted to A&A after the first referee report

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• Ionizing Radiation Escape from Low-Redshift Galaxies and Its Connection to Cosmic Reionization
• The Lyman-alpha and Continuum Origins Survey II: the connection between the escape of ionizing radiation and Lyman-alpha halos in star-forming galaxies
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