The THESAN project: Lyman-alpha emitters as probes of ionized bubble sizes

Abstract

We use the THESAN radiation-hydrodynamics simulations to investigate how Lyman-$\hat{I}\pm$ emitters (LAEs) trace ionized bubble sizes during the Epoch of Reionization. We generate realistic LAE catalogs by combining accurate intrinsic Ly$\hat{I}\pm$ production and intergalactic transmission with an empirical model for dust absorption and gas outflows. By calibrating to observationally-constrained Ly$\hat{I}\pm$ luminosity functions, we reproduce the rapid decline in Ly$\hat{I}\pm$ visibility toward higher redshifts while revealing mild tensions in LAE fractions near the end of reionization. Before the midpoint of reionization, galaxies within larger line-of-sight bubbles ($\gtrsim 10$ cMpc) have higher observed Ly$\hat{I}\pm$ luminosity and equivalent width (EW), demonstrating that the evolving LAE fraction provides a practical statistical tracer for bubble size. These correlations weaken as percolation progresses and the IGM becomes increasingly ionized. In LAE selected samples with $L_{\text{Ly}\hat{I}\pm }>10^{41.5}{\text{erg s}}^{-1}$, Ly$\hat{I}\pm$ properties correlate with bubble size more strongly than UV magnitude, especially at $z\gtrsim 7$. This simulation-based framework maps LAE selections to bubble-size statistics, clarifies biases in more idealized models, and will supply public catalogs to interpret current and forthcoming JWST and narrow-band LAE surveys in terms of the evolving topology of reionization.

18 pages, 18 figures. Published in the Open Journal of Astrophysics