New observations of z~7 galaxies: evidence for a patchy reionization
  We present new results from our search for z~7 galaxies from deep
spectroscopic observations of candidate z-dropouts in the CANDELS fields.
Despite the extremely low flux limits achieved by our sensitive observations,
only 2 galaxies have robust redshift identifications, one from its Lyalpha
emission line at z=6.65, the other from its Lyman-break, i.e. the continuum
discontinuity at the Lyalpha wavelength consistent with a redshift 6.42, but
with no emission line. In addition, for 23 galaxies we present deep limits in
the Lyalpha EW derived from the non detections in ultra-deep observations.
Using this new data as well as previous samples, we assemble a total of 68
candidate z~7 galaxies with deep spectroscopic observations, of which 12 have a
line detection. With this much enlarged sample we can place solid constraints
on the declining fraction of Ly$\alpha$ emission in z~7 Lyman break galaxies
compared to z~6, both for bright and faint galaxies. Applying a simple
analytical model, we show that the present data favor a patchy reionization
process rather than a smooth one.
