Model-independent evidence in favour of an end to reionization by z โ 6
Model-independent evidence in favour of an end to reionization by z โ 6
We present new upper limits on the volume-weighted neutral hydrogen fraction, <xHI>, at z~5-6 derived from spectroscopy of bright quasars. The fraction of the Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides the only model-independent upper limit on <xHI>, requiring no assumptions about the physical conditions in โฆ