Neutral island statistics during reionization from 21-cm tomography
  We present the prospects of extracting information about the Epoch of
Reionization by identifying the remaining neutral regions, referred to as
islands, in tomographic observations of the redshifted 21-cm signal. Using
simulated data sets we show that at late times the 21-cm power spectrum is
fairly insensitive to the details of the reionization process but that the
properties of the neutral islands can distinguish between different
reionization scenarios. We compare the properties of these islands with those
of ionized bubbles. At equivalent volume filling fractions, neutral islands
tend to be fewer in number but larger compared to the ionized bubbles. In
addition, the evolution of the size distribution of neutral islands is found to
be slower than that of the ionized bubbles and also their percolation behaviour
differs substantially. Even though the neutral islands are relatively rare,
they will be easier to identify in observations with the low-frequency
component of the Square Kilometre Array (SKA-Low) due to their larger size and
the lower noise levels at lower redshifts. The size distribution of neutral
islands at the late stages of reionization is found to depend on the source
properties, such as the ionizing efficiency of the sources and their minimum
mass. We find the longest line of sight through a neutral region to be more
than 100 comoving Mpc until very late stages (90-95 per cent reionized), which
may have relevance for the long absorption trough at $z=5.6-5.8$ in the
spectrum of quasar ULAS J0148+0600.
