We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO/VLT for the confirmation of z \simeq 7 “ z–band dropout ” candidates selected from our VLT/Hawk-I imaging survey over three independent fields .
In particular we report on two newly discovered galaxies at redshift \sim 6.7 in the NTT deep field : both galaxies show a Ly \alpha emission line with rest-frame EWs of the order 15-20Å and luminosities of 2-4 \times 10 ^ { 42 } ergs ^ { -1 } .
We also present the results of ultra-deep observations of a sample of i-dropout galaxies , from which we set a solid upper limit on the fraction of interlopers .

Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.7 < z < 7.1 .
This is systematically below the expectations drawn on the basis of lower redshift observations : in particular there is a significant lack of objects with intermediate Ly \alpha EWs ( between 20 and 55 Å ) .
We conclude that the trend for the fraction of Ly \alpha emission in LBGs that is constantly increasing from z \sim 3 to z \sim 6 is most probably reversed from z \sim 6 to z \sim 7 .
Explaining the observed rapid change in the LAE fraction among the drop-out population with reionization requires a fast evolution of the neutral fraction of hydrogen in the Universe .
Assuming that the Universe is completely ionized at z=6 and adopting the semi-analytical models of Dijkstra et al .
( 2011 ) , we find that our data require a change of the neutral hydrogen fraction of the order \Delta \chi _ { HI } \sim 0.6 in a time \Delta z \sim 1 , provided that the escape fraction does not increase dramatically over the same redshift interval .