From Mirrors to Windows: Lyman-Alpha Radiative Transfer in a Very Clumpy
  Medium
  Lyman-Alpha (Ly$\alpha$) is the strongest emission line in the Universe and
is frequently used to detect and study the most distant galaxies. Because Lya
is a resonant line, photons typically scatter prior to escaping; this
scattering process complicates the interpretation of Ly$\alpha$ spectra, but
also encodes a wealth of information about the structure and kinematics of
neutral gas in the galaxy. Modeling the Ly$\alpha$ line therefore allows us to
study tiny-scale features of the gas, even in the most distant galaxies.
Curiously, observed Ly$\alpha$ spectra can be modeled successfully with very
simple, homogeneous geometries (such as an expanding, spherical shell), whereas
more realistic, multiphase geometries often fail to reproduce the observed
spectra. This seems paradoxical since the gas in galaxies is known to be
multiphase. In this Letter, we show that spectra emerging from extremely clumpy
geometries with many clouds along the line of sight converge to the predictions
from simplified, homogeneous models. We suggest that this resolves the apparent
discrepancy, and may provide a way to study the gas structure in galaxies on
scales far smaller than can be probed in either cosmological simulations or
direct (i.e., spatially-resolved) observations.
