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Title: Rapid decline of Lyα emission toward the reionization era

The observed deficit of strongly Lyα emitting galaxies at z > 6.5 is attributed to 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 Lyα fraction at z ∼ 8 using two methods. First, we derived N {sub Lyα}/N {sub tot} directly, using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al.) that compares the z > 7 galaxy spectra to models of the Lyα equivalent width (W {sub Lyα}) distribution at z ∼ 6. We explored two simple evolutionary scenarios: pure number evolution where Lyα 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 Lyα 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 Lyα fractionmore » has dropped by a factor of >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. A comparison of our results with theoretical models implies the IGM volume averaged neutral hydrogen fraction ≳ 0.3, suggesting that we are likely witnessing reionization in progress at z ∼ 8.« less
Authors:
;  [1] ; ;  [2] ;  [3] ;  [4] ; ;  [5] ;  [6] ;  [7]
  1. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A and M University, College Station, TX 77845 (United States)
  2. Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States)
  3. Department of Statistics, Texas A and M, College Station, TX 77845 (United States)
  4. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
  5. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
  6. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
  7. Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
Publication Date:
OSTI Identifier:
22370528
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 794; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; DISTRIBUTION; EMISSION; EVOLUTION; GALAXIES; HYDROGEN; INFRARED SPECTRA; LIMITING VALUES; LYMAN LINES; OPACITY; RED SHIFT; SIMULATION; TELESCOPES; UNIVERSE