Astraeus VIII: A new framework for Lyman-$\alpha$ emitters applied to different reionisation scenarios

Abstract

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

25 pages, 9 figures; accepted for publication in MNRAS

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• The impact of an evolving stellar initial mass function on early galaxies and reionisation
• JADES: The star-formation and chemical enrichment history of a luminous galaxy at z~9.43 probed by ultra-deep JWST/NIRSpec spectroscopy
• JADES: Primaeval Lyman-$\alpha$ emitting galaxies reveal early sites of reionisation out to redshift $z\sim 9$
• Euclid preparation. The Cosmic Dawn Survey (DAWN) of the Euclid Deep and Auxiliary Fields
• Simulation-Based Inference of the sky-averaged 21-cm signal from CD-EoR with REACH
• Mapping reionization bubbles in the JWST era II: inferring the position and characteristic size of individual bubbles
• The 21cm-galaxy cross-correlation: Realistic forecast for 21cm signal detection and reionisation constraints
• Mapping neutral islands during end stages of reionization with photometric intergalactic medium tomography
• Deep JWST spectroscopy of galaxies in a candidate ionized bubble at $z=8.7$: probing reionization at pMpc scales with Ly$\alpha$ emission