Quasar Ionization Front Ly{\alpha} Emission in an Inhomogeneous
  Intergalactic Medium
  The conditions within the ionization front of a quasar during reionization (T
~ 30,000 K, neutral hydrogen fraction ~ 0.5) are ideal for producing
Lyman-alpha emission via collisional excitation of hydrogen atoms. Observations
of this emission, which could subtend >10 arcmin$^2$ on the sky, would
definitively demonstrate the presence of a neutral intergalactic medium at the
observed epoch, placing valuable constraints on the progress of reionization.
We find that the expected Lyman-alpha surface brightness is significantly
weaker than previously determined and may be impossible to observe with current
and near-future instruments. Past work calculated the Lyman-alpha emission from
a quasar ionization front in a homogeneous medium with a clumping factor
approximation to account for inhomogeneities. We find using 1D radiative
transfer calculations that this approximation overestimates the emission by a
factor of >3. Our calculations model the propagation of ionizing photons and
compute the Lyman-alpha emission from quasar ionization fronts on sightlines
from a hydrodynamic cosmological simulation at z = 7.1. To better understand
the physical properties of the emission, we also develop an analytic model that
accurately describes the results of the full radiative transfer calculation.
