No Evidence for Lyman-alpha Emission in Spectroscopy of z > 7 Candidate
  Galaxies
  We present Gemini/GNIRS spectroscopic observations of 4 z-band (z~7) dropout
galaxies and VLT/XSHOOTER observations of one z-band dropout and 3 Y-band
(z~8-9) dropout galaxies in the Hubble Ultra Deep Field, which were selected
with Wide Field Camera 3 imaging on the Hubble Space Telescope. We find no
evidence of Lyman-alpha emission with a typical 5-sigma sensitivity of
5X10^-18erg/cm^2/s, and we use the upper limits on Lyman-alpha flux and the
broad-band magnitudes to constrain the rest-frame equivalent widths for this
line emission. Accounting for incomplete spectral coverage, we survey 3.0
z-band dropouts and 2.9 Y-band dropouts to a Lyman-alpha rest-frame equivalent
width limit > 120Ang (for an unresolved emission line); for an equivalent width
limit of 50Ang the effective numbers of drop-outs surveyed fall to 1.2 z-band
drop-outs and 1.5 Y-band drop-outs. A simple model where the fraction of high
rest-frame equivalent width emitters follows the trend seen at z=3-6.5 is
inconsistent with our non-detections at z=7-9 at the ~ 1-sigma level for
spectrally unresolved lines, which may indicate that a significant neutral HI
fraction in the intergalactic medium suppresses the Lyman-alpha line in z-drop
and Y-drop galaxies at z > 7.
