Constraints on the End of Reionization from the Density Fields
  Surrounding Two Highly Opaque Quasar Sightlines
  The observed large-scale scatter in Lyman $\alpha$ opacity of the
intergalactic medium at $z<6$ implies large fluctuations in the neutral
hydrogen fraction that are unexpected long after reionization has ended. A
number of models have emerged to explain these fluctuations that make testable
predictions for the relationship between Ly$\alpha$ opacity and density. We
present selections of $z=5.7$ Ly$\alpha$-emitting galaxies (LAEs) in the fields
surrounding two highly opaque quasar sightlines with long Ly$\alpha$ troughs.
The fields lie towards the $z=6.0$ quasar ULAS J0148+0600, for which we
re-analyze previously published results using improved photometric selection,
and towards the $z=6.15$ quasar SDSS J1250+3130, for which results are
presented here for the first time. In both fields, we report a deficit of LAEs
within 20 $h^{-1}$ Mpc of the quasar. The association of highly opaque
sightlines with galaxy underdensities in these two fields is consistent with
models in which the scatter in Ly$\alpha$ opacity is driven by large-scale
fluctuations in the ionizing UV background, or by an ultra-late reionization
that has not yet concluded at $z=5.7$.
