Model-independent evidence in favour of an end to reionization by z ≈ 6. Issue 1 (18th December 2014)

• Record Type: Journal Article
• Authors: McGreer, Ian D.; Mesinger, Andrei; D'Odorico, Valentina
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 447:Issue 1(2015)
• Page Start: 499
• Page End: 505
• Publication Date: 2014-12-18
• Subjects: galaxies: high-redshift -- quasars: absorption lines -- cosmology: observations -- dark ages, reionization, first stars -- diffuse radiation -- early Universe; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stu2449
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract : We present new upper limits on the volume-weighted neutral hydrogen fraction, $\bar{x}_{\rm H\, \small {i}}$, at z ∼ 5–6 derived from spectroscopy of bright quasars. The fraction of the Lyα and Lyβ forests that is 'dark' (with zero flux) provides the only model-independent upper limit on $\bar{x}_{\rm H\, \small {i}}$, requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work, we update our previous results using a larger sample (22 objects) of medium-depth (∼ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on $\bar{x}_{\rm H\, \small {i}}$ derived from dark pixel analysis to $\bar{x}_{\rm H\, \small {i}}\le 0.06{+0.05 (1\sigma )}$ at z = 5.9 and $\bar{x}_{\rm H\, \small {i}}\le 0.04{+0.05 (1\sigma )}$ at z = 5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z ≈ 6.