CANDELSz7: a large spectroscopic survey of CANDELS galaxies in the
  reionization epoch
  We present the results of CANDELSz7, an ESO large program aimed at confirming
spectroscopically a homogeneous sample of z~6 and z~7 star forming galaxies.
The candidates were selected in the GOODS-South, UDS and COSMOS fields using
the official CANDELS catalogs based on H160-band detections. Standard color
criteria, which were tailored depending on the ancillary multi-wavelength data
available for each field, were applied to select more than 160 candidate
galaxies at z~6 and z~7. Deep medium resolution FORS2 spectroscopic
observations were then conducted with integration times ranging from 12 to 20
hours, to reach a Lyalpha flux limit of approximately 1-3x 10-18 erg/s/cm^2 at
3sigma. For about 40% of the galaxies we could determine a spectroscopic
redshift, mainly through the detection of a single emission line that we
interpret as Lyalpha emission, or for some of the brightest objects (H160<
25.5) from the presence of faint continuum and sharp drop that we interpret as
a Lyman break. In this paper we present the redshifts and main properties of 65
newly confirmed high redshift galaxies. Adding previous proprietary and
archival data we assemble a sample of ~260 galaxies that we use to explore the
evolution of the Lyalpha fraction in Lyman break galaxies and the change in the
shape of the emission line between z~6 and z~7. We also discuss the accuracy of
the CANDELS photometric redshifts in this redshift range.
