Optical-NIR spectra of quasars close to reionization (z~ 6)
  X-shooter, with its characteristics of resolution, spectral coverage and efficiency, provides a unique opportunity to obtain spectra of the highest-redshift quasars (z ~ 6) that will allow us to carry out successful investigations on key cosmological issues, from the details of the re-ionization process, to the evolution of the first galaxies and AGNs. In this paper, we present the spectra of three z ~ 6 quasars: one obtained during the commissioning of X-shooter and two in the context of our ongoing GTO programme. Combining this sample with data in the literature, we update the value of the C IV cosmic mass density in the range 4.5 < z < 5, confirming the constant trend with redshift between 2.5 and 5. 
V. D'Odorico, G. Cupani, S. Cristiani, R. Maiolino, P. Molaro, M.   Nonino, A. Cimatti, S. di Serego Alighieri, F. Fiore, A....
astro-ph.CO