MOS spectroscopy of protocluster candidate galaxies at z=6.5
  The epoch corresponding to a redshift of z $\sim 6.5$ is close to full
re-ionisation of the Universe, and early enough to provide an intriguing
environment to observe the early stage of large-scale structure formation. It
is also en epoch that can be used to verify the abundance of a large population
of low luminosity star-forming galaxies, that are deemed responsible for cosmic
re-ionisation. Here, we present the results of follow-up multi-object
spectroscopy using OSIRIS at Gran Telescopio Canarias (GTC) of 16 Ly$\alpha$
emitter (LAE) candidates discovered in the Subaru/XMM Newton Deep Survey. We
have securely confirmed 10 LAEs with sufficient signal-to-noise ratio of the
Ly$\alpha$ emission line. The inferred star formation rates of the confirmed
LAEs are on the low side, within the range 0.9-4.7 M$_{\odot}$ yr$^{-1}$.
However, they show relatively high Ly$\alpha$ rest frame equivalent widths.
Finally we have shown that the mechanical energy released by the star formation
episodes in these galaxies is enough to create holes in the neutral hydrogen
medium such that Lyman continuum photons can escape to the intergalactic
medium, thus contributing to the re-ionisation of the Universe.
