Speaker
Description
With the James Web Telescope (JWST) offering a prime opportunity to observe Lyman-alpha (Lya) in the high-redshift Universe, understanding the information embedded in Lya observables and its relation to ionizing radiation has become a crucial task in the study of the Epoch of Reionization. Since Lya is sensitive to gas density, dust, and fragmentation, it provides vital information about the interstellar medium (ISM) and the circumgalactic medium (CGM). Deciphering this information remains a complex challenge due to Lya resonant nature and complex radiative transfer effects. Current isotropic radiative transfer models reproduce the line profile but lack clarity on how fitted parameters relate to actual physical conditions. For more accurate modeling, we must consider key features necessary for Lya and Lyman-Continuum (LyC) radiation escape: astrophysical gas is anisotropic and multiphase.
In this talk, I will discuss the results of Monte Carlo radiative transfer simulations of Lya performed on an anisotropic setting: a slab with an empty channel carved in the neutral gas distribution. Regardless of the setup simplicity, the results are counterintuitive and far from simple. Given the large line-center optical depth of the slab, one would expect that most Lya photons escape through the empty channel. Our numerical results show, in contrast, that only a fraction of photons escape. To explain this dilemma, we developed an analytical model describing Lya photons' general scattering and transmission behavior. Our findings show a much greater number of scatterings per reflection, leading to an overall much greater transmission probability through the slab. These results imply that Lya photons are surprisingly not as biased to the 'path of least resistance' and can trace an averaged hydrogen distribution rather than only low-column densities. Time provided, I will also discuss the implications of this result when interpreting the observed Lya profiles, specifically, when used as a tracer for ionizing photons.
