Model-independent evidence in favour of an end to reionization by z ≈ 6

• DOI: 10.1093/mnras/stu2449
• Publication Date: 2014-12-19T06:08:24Z
• Authors: Ian D. McGreer; Andrei Mesinger; Valentina D'Odorico
• Keywords: Lyman-alpha forest; Lyman limit; Sigma

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 Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides only model-independent limit requiring no assumptions about physical conditions in intergalactic medium or quasar's unabsorbed UV continuum. In this work we update our previous results using a larger sample (22 objects) medium-depth (~ few hours) spectra high-redshift quasars obtained with Magellan, MMT, VLT. This significantly improves bound <xHI> dark pixel analysis to <= 0.06 + 0.05 (1{\sigma}) z=5.9, 0.04 z=5.6. These provide robust constraints for theoretical models reionization, strongest available evidence reionization has completed (or very nearly complete) by z~6.