Resonant-line radiative transfer within power-law density profiles
  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.
