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Unpublished Paper
Rapid Decline of Lyman-α Emission Toward the Reionization Era
The Astrophysical Journal (2014)
  • V. Tilvi
  • C. Papovich
  • H.C. Ferguson
  • S.L. Finkelstein
  • J. Long
  • M. Song
  • M. Dickinson
  • A.M. Koekemoer
  • Mauro Giavalisco, University of Massachusetts - Amherst
  • B. Mobasher
The observed deficit of strongly Lyman-α emitting galaxies at z > 6.5 is attributed to either increasing neutral hydrogen in the intergalactic medium (IGM) and/or to the evolving galaxy properties. To investigate this, we have performed very deep near-IR spectroscopy of z ≳7 galaxies using MOSFIRE on the Keck-I Telescope. We measure the Lyman-α fraction at z ∼ 8 using two methods. First, we derived NLy_/Ntot directly using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al. 2012) that compares the z > 7 galaxy spectra to models of the Lyman-α equivalent width (WLy_) distribution at z ∼ 6. We explored two simple evolutionary scenarios: pure number evolution where Lyman-α is blocked in some fraction of galaxies (perhaps due to the IGM being opaque along only some fraction of sightlines) and uniform dimming evolution where Lyman-α is attenuated in all galaxies by a constant factor (perhaps owing to processes from galaxy evolution or a slowly increasing IGM opacity). The Bayesian formalism places stronger constraints compared with the direct method. Combining our data with that in the literature we find that at z ∼ 8 the Lyman-α fraction has dropped by a factor >3 (84% confidence interval) using both the dimming and number evolution scenarios, compared to the z ∼ 6 values. Furthermore, we find a tentative “positive” Bayesian evidence favoring the number evolution scenario over dimming evolution, extending trends observed at z . 7 to higher redshift. Comparison of our results with theoretical models imply the IGM volume averaged neutral hydrogen fraction & 0.3 suggesting that we are likely witnessing reionization in progress at z ∼ 8.
Publication Date
September 17, 2014
Prepublished version downloaded from ArXiv. Published version is located at
Citation Information
V. Tilvi, C. Papovich, H.C. Ferguson, S.L. Finkelstein, et al.. "Rapid Decline of Lyman-α Emission Toward the Reionization Era" The Astrophysical Journal (2014)
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