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THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). III. A CENSUS OF Lyα EMISSION AT z ≳ 7 FROM HST SPECTROSCOPY

  • Author(s): Schmidt, KB
  • Treu, T
  • Bradač, M
  • Vulcani, B
  • Huang, KH
  • Hoag, A
  • Maseda, M
  • Guaita, L
  • Pentericci, L
  • Brammer, GB
  • Dijkstra, M
  • Dressler, A
  • Fontana, A
  • Henry, AL
  • Jones, TA
  • Mason, C
  • Trenti, M
  • Wang, X
  • et al.
Abstract

© 2016. The American Astronomical Society. All rights reserved. We present a census of Lyα emission at z ≳ 7, utilizing deep near-infrared Hubble Space Telescope grism spectroscopy from the first six completed clusters of the Grism Lens-Amplified Survey from Space (GLASS). In 24/159 photometrically selected galaxies we detect emission lines consistent with Lyα in the GLASS spectra. Based on the distribution of signal-to-noise ratios and on simulations, we expect the completeness and the purity of the sample to be 40%-100% and 60%-90%, respectively. For the objects without detected emission lines we show that the observed (not corrected for lensing magnification) 1σ flux limits reach 5 × 10-18erg s-1cm-2per position angle over the full wavelength range of GLASS (0.8-1.7 μm). Based on the conditional probability of Lyα emission measured from the ground at z ∼ 7, we would have expected 12-18 Lyα emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Lyα emission with respect to z ∼ 6. Deeper follow-up spectroscopy, here exemplified by Keck spectroscopy, is necessary to improve our estimates of completeness and purity and to confirm individual candidates as true Lyα emitters. These candidates include a promising source at z = 8.1. The spatial extent of Lyα in a deep stack of the most convincing Lyα emitters with 'z' = 7.2 is consistent with that of the rest-frame UV continuum. Extended Lyα emission, if present, has a surface brightness below our detection limit, consistent with the properties of lower-redshift comparison samples. From the stack we estimate upper limits on rest-frame UV emission line ratios and find fC IV/fLyα≳ 0.32 and fC III/fLyα≳ 0.32, in good agreement with other values published in the literature.

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