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We use the astraeus framework to investigate how the visibility and spatial distribution of Lyman-α (Lyα) emitters (LAEs) during reionization is sensitive to a halo mass-dependent fraction of ionizing radiation escaping from the galactic environment (f esc) and the ionization topology. To this end, we consider the two physically plausible bracketing scenarios of f esc increasing and decreasing with rising halo mass. We derive the corresponding observed Lyα luminosities of galaxies for three different analytic Lyα line profiles and associated Lyα escape fraction (⁠|$f_\mathrm{esc}^\mathrm{Ly\alpha }$|⁠) models: importantly, we introduce two novel analytic Lyα line profile models that describe the surrounding interstellar medium (ISM) as dusty gas clumps. They are based on parameterizing results from radiative transfer simulations, with one of them relating |$f_\mathrm{esc}^\mathrm{Ly\alpha }$| to f esc by assuming the ISM of being interspersed with low-density tunnels. Our key findings are: (i) for dusty gas clumps, the Lyα line profile develops from a central to double peak dominated profile as a galaxy's halo mass increases; (ii) LAEs are galaxies with |$M_h\gtrsim 10^{10}\, {\rm \rm M_\odot }$| located in overdense and highly ionized regions; (iii) for this reason, the spatial distribution of LAEs is primarily sensitive to the global ionization fraction and only weakly in second-order to the ionization topology or a halo mass-dependent f esc; (iv) furthermore, as the observed Lyα luminosity functions reflect the Lyα emission from more massive galaxies, there is a degeneracy between the f esc-dependent intrinsic Lyα luminosity and the Lyα attenuation by dust in the ISM if f esc does not exceed |$\sim 50~{{\ \rm per \, cent}}$|⁠. [ABSTRACT FROM AUTHOR]

In this work, the sixth of a series, we use the seminumerical rAdiative tranSfer coupling of galaxy formaTion and Reionization in N -body dark-matter simUlationS (astraeus) framework to investigate the nature of the sources that reionized the Universe. We extend astraeus , which already couples a galaxy formation semi-analytical model with a detailed seminumerical reionization scheme, to include a model for black-hole formation, growth, and the production of ionizing radiation from associated active galactic nuclei (AGNs). We calibrate our fiducial AGN model to reproduce the bolometric luminosity function at z ≃ 5, and explore the role of the resulting AGN population in reionizing the Universe. We find that in all the models yielding a reasonable AGN luminosity function, galaxies dominate overwhelmingly the ionizing budget during the Epoch of Reionization, with AGN accounting for 1–10 per cent of the ionizing budget at z  = 6 and starting to play a role only below z ≲ 5. [ABSTRACT FROM AUTHOR]

Low-mass galaxies are thought to provide the bulk of the ionizing radiation necessary to reionize the Universe. The amount of photons escaping the galaxies is poorly constrained theoretically, and difficult to measure observationally. Yet it is an essential parameter of reionization models. We study in detail how ionizing radiation can leak from high-redshift galaxies. For this purpose, we use a series of high-resolution radiation hydrodynamics simulations, zooming on three dwarf galaxies in a cosmological context. We find that the energy and momentum input from the supernova explosions has a pivotal role in regulating the escape fraction by disrupting dense star-forming clumps, and clearing sightlines in the halo. In the absence of supernovae, photons are absorbed very locally, within the birth clouds of massive stars. We follow the time evolution of the escape fraction and find that it can vary by more than six orders of magnitude. This explains the large scatter in the value of the escape fraction found by previous studies. This fast variability also impacts the observability of the sources of reionization: a survey even as deep as M1500 = -14 would miss about half of the underlying population of Lyman-continuum emitters. [ABSTRACT FROM AUTHOR]