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A luminous quasar at a redshift of z = 7.085


The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed1 by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified2,3,4 in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 1013L and hosts a black hole with a mass of 2 × 109M (where L and M are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing5, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

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Figure 1: Spectrum of ULAS J1120+0641 and a composite spectrum derived from lower redshift quasars.
Figure 2: The observed Lyα absorption measured towards ULAS J1120+0641 and two lower-redshift quasars.
Figure 3: The inferred Lyα near-zone transmission profile of ULAS J1120+0641 compared to those of two lower-redshift quasars.
Figure 4: Rest-frame transmission profile of ULAS J1120+0641 in the region of the Lyα emission line, compared to several damping profiles.


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M.P. acknowledges support from the University of London’s Perren Fund. P.C.H. and R.G.McM. acknowledge support from the STFC-funded Galaxy Formation and Evolution programme at the Institute of Astronomy. X. Fan and R. White supplied spectra of the SDSS quasars. M. Haehnelt provided insights into quasar near-zone physics. The staffs of the Joint Astronomy Centre, the Cambridge Astronomical Survey Unit and the Wide-Field Astronomy Unit, Edinburgh, all made vital contributions to the UKIDSS project. The support staff at the Gemini North Telescope, particularly K. Roth, provided assistance with the Gemini observations. This work is based in part on data obtained from UKIDSS, SDSS, the Liverpool Telescope, the Isaac Newton Telescope, the Gemini Observatory and the European Southern Observatory.

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Authors and Affiliations



D.J.M., S.J.W., M.P., B.P.V., P.C.H., R.G.McM. and C.S. identified ULAS J1120+0641 and obtained the follow-up observations. S.J.W., P.C.H., D.J.M., T.T., B.P.V., R.G.McM. and M.P. analysed the follow-up observations and interpreted the results. A.A., S.D., E.A.G.-S., N.C.H., P.H., M.J.I. and A.L. obtained, analysed and disseminated the UKIDSS data. E.K. and H.J.A.R. obtained the FORS2 spectrum of ULAS J1120+0641. D.J.M. and S.J.W. wrote the manuscript, into which all other authors had input.

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Correspondence to Daniel J. Mortlock.

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Mortlock, D., Warren, S., Venemans, B. et al. A luminous quasar at a redshift of z = 7.085. Nature 474, 616–619 (2011).

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