摘要：We present a 30 h integration Very Large Telescope X-shooter spectrum of the Lyman series forest towards the z = 7.084 quasar ULAS J1120+0641. The only detected transmission at S/N > 5 is confined to seven narrow spikes in the Lyα forest, over the redshift range 5.858 5.5. The data nevertheless provide only a weak limit on the volume-weighted intergalactic medium (IGM) hydrogen neutral fraction at z ~ 6.5, xH i > 10-4, similar to limits at redshift z ~ 6 from less distant quasars. The new observations cannot extend measurements of the neutral fraction of the IGM to higher values because absorption in the Lyα forest is already saturated near z ~ 6. For higher neutral fractions, other methods such as measuring the red damping wing of the IGM will be required.
