VLT optical and near-infrared observations of the z=6.28 quasar SDSS J1030+0524

We present new VLT spectroscopic observations of the most distant quasar known, SDSS J1030+0524 at z = 6.28, which was recently discovered by the Sloan Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough caused by neutral hydrogen in the intergalactic medium. There is no detectable flux over the wavelength range from 8450 to 8710 Angstrom. We set a stronger limit on the drop of the flux level blue-ward of the Lyalpha line: a factor of more than 200. Below 8450 Angstrom the spectrum shows a rise in flux, with a large fraction ( > 60%) of the total emission produced by a few narrow features of transmitted flux. We discuss the proximity effect around this quasar, with the presence of transmitted flux with many absorption features in a region of about 23 h(-1) comoving Mpc. If we assume that the surrounding medium is completely neutral, the size of this region would imply a quasar lifetime of similar to1.3 x 10(7) yr. We also present near-IR spectroscopy of both SDSS J1030+0524 and SDSS J1306+05, the second most distant quasar known, at redshift 6.0. We combine measurements of the C IV line and limits on the He II emission from the near-IR spectra with the N v line measurements from the optical spectra to derive the metal abundances of these early quasar environments. The results are indistinguishable from those of lower redshift quasars and indicate little or no evolution in the metal abundances from z similar to 6 to 2. The line ratios suggest supersolar metallicities, implying that the first stars around the quasars must have formed at least a few hundreds of megayears prior to the observation, i.e., at redshifts higher than 8.