Jonathan R. Pritchard (CfA), Avi Loeb (CfA), Stuart Wyithe (Melbourne)

In this talk, we explore the constraints on the reionization history
that are provided by current observations of the Ly-alpha forest and
the CMB. Rather than use a particular semi-analytic model, we take the
novel approach of parametrizing the ionizing sources with arbitrary
functions, and perform likelihood analyses to constrain possible
reion- ization histories. We find model independent conclusions that
reionization is likely to be mostly complete by z = 8 and that the IGM
was 50% ionized at z = 9 - 10.  Upcoming low-frequency observations of
the redshifted 21 cm line of neutral hydrogen are expected to place
significantly better constraints on the hydrogen neutral fraction at 6