Resonant-line radiative transfer within power-law density profiles

TL;DR

This paper develops new analytic solutions and numerical methods for modeling Lyman-alpha radiative transfer in galaxies with power-law density profiles, enhancing understanding of galaxy formation and evolution.

Contribution

It introduces a closed-form analytic solution for resonant-line radiative transfer in power-law density profiles and verifies it with a novel gridless Monte Carlo method.

Findings

Analytic solutions for Lya radiative transfer in power-law profiles.

Validated numerical Monte Carlo method for complex radiative transfer scenarios.

Insights into the connection between gas environments and galaxy observations.

Abstract

Star-forming regions in galaxies are surrounded by vast reservoirs of gas capable of both emitting and absorbing Lyman-alpha (Lya) radiation. Observations of Lya emitters and spatially extended Lya haloes indeed provide insights into the formation and evolution of galaxies. However, due to the complexity of resonant scattering, only a few analytic solutions are known in the literature. We discuss several idealized but physically motivated scenarios to extend the existing formalism to new analytic solutions, enabling quantitative predictions about the transport and diffusion of Lya photons. This includes a closed form solution for the radiation field and derived quantities including the emergent flux, peak locations, energy density, average internal spectrum, number of scatters, outward force multiplier, trapping time, and characteristic radius. To verify our predictions, we employ a robust gridless Monte Carlo radiative transfer (GMCRT) method, which is straightforward to incorporate into existing ray-tracing codes but requires modifications to opacity-based calculations, including dynamical core-skipping acceleration schemes. We primarily focus on power-law density and emissivity profiles, however both the analytic and numerical methods can be generalized to other cases. Such studies provide additional intuition and understanding regarding the connection between the physical environments and observational signatures of galaxies throughout the Universe.