The THESAN project: Lyman-a emitter luminosity function calibration

The observability of Ly aemitting galaxies (LAEs) during the Epoch of Reionization can provide a sensitive probe of the evolving neutral hydrogen gas distribution, thus setting valuable constraints to distinguish different reionization models. In this study, we utilize the new THESAN suite of large-volume ( L (box) = 95.5 cMpc) cosmological radiation-hydrodynamic simulations to directly model the Lyaemission from individual galaxies and the subsequent transmission through the intergalactic medium. THESAN combines the AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation model and includes high- and medium-resolution simulations designed to investigate the impacts of halo-mass-dependent escape fractions, alternative dark matter models, and numerical convergence. We find important differences in the Lyatransmission based on reionization history, bubble morphology, frequency offset from line centre, and galaxy brightness. For a given global neutral fraction, Lyatransmission reduces when low-mass haloes dominate reionization over high-mass haloes. Furthermore, the variation across sightlines for a single galaxy is greater than the variation across all galaxies. This collectively affects the visibility of LAEs, directly impacting observed Lyaluminosity functions (LFs). We employ Gaussian Process Regression using SWIFTEMULATOR to rapidly constrain an empirical model for dust escape fractions and emergent spectral-line profiles to match observed LFs. We find that dust strongly impacts the Lyatransmission and covering fractions of M UV less than or similar to -19 galaxies in M vi greater than or similar to 1011 M-circle dot haloes, such that the dominant mode of removing Lyaphotons in non-LAEs changes from low-IGM transmission to high dust absorption around z similar to 7.

Automated summary

Through simulations, we have discovered the impact of galaxies on photon transmission, as well as the significant differences in Lyα transmission based on galaxy brightness and reionization history. This study is important for understanding the observability of Lyα emitting galaxies during the Epoch of Reionization and their role in different reionization models.