Lyα Radiative Transfer in Cosmological Simulations and Application to az≃ 8 Lyα Emitter

Abstract

We develop an Lyα radiative transfer (RT) Monte Carlo code for cosmological simulations. High resolution, along with appropriately treated cooling, can result in simulated environments with very high optical depths. Thus, solving the Lyα RT problem in cosmological simulations can take an unrealistically long time. For this reason, we develop methods to speed up the Lyα RT. With these accelerating methods, along with the parallelization of the code, we make the problem of Lyα RT in the complex environments of cosmological simulations tractable. We test the RT code against simple Lyα emitter models, and then we apply it to the brightest Lyα emitter of a gasdynamics+N-body adaptive refinement tree (ART) simulation at z ≃ 8. We find that recombination rather than cooling radiation Lyα photons is the dominant contribution to the intrinsic Lyα luminosity of the emitter, which is ≃4.8 × 1043 ergs s-1. The size of the emitter is pretty small, making it unresolved for currently available instruments. Its spectrum before adding the Lyα Gunn-Peterson absorption (GPA) resembles that of static media, despite some net inward radial peculiar motion. This is because for such high optical depths as those in ART simulations, velocities of order some hundreds of kilometers per second are not important. We add the GPA in two ways: (1) we assume no damping wing, corresponding to the situation where the emitter lies within the H II region of a very bright quasar, and (2) we allow for the damping wing. Including the damping wing leads to a maximum line brightness suppression by roughly a factor of ~62. The line fluxes, even though quite faint for current ground-based telescopes, should be within reach for JWST.