Discovery of a redshift 6.13 quasar in the UKIRT infrared deep sky survey

D. J. Mortlock, M. Patel, S. J. Warren, B. P. Venemans, R. G. McMahon, P. C. Hewett, C. Simpson, R. G. Sharp, B. Burningham, S. Dye, S. Ellis, E. A. Gonzales-Solares, N. Huélamo

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Optical and near-infrared (NIR) spectra are presented for ULAS J131911.29+095051.4(hereafter ULAS J1319+0950), a new redshift z = 6.127 ± 0.004 quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared Deep Sky Survey (UKIDSS). The source has Yvega = 19.10 ± 0.03, corresponding to M1450, AB= -27.12, which is comparable to the absolute magnitudes of the ≃ 6 quasars discovered in the Sloan Digital Sky Survey (SDSS). ULAS J1319+0950, in fact, registered by SDSS as a faint source with zAB= 20.13 ± 0.12, just below the signal-to-noise ratio limit of the SDSS high-redshift quasar survey. The faint Z-band magnitude is a consequence of the weak Ly α/N v emission line, which has a rest-frame equivalent width of ∼20Å and provides only a small boost to the z-band flux. Nevertheless, there is no evidence of a significant new population of high-redshift quasars with weak emission lines from this UKIDSS-based search. The Ly?α?optical depth to ULAS J1319+0950 is consistent with that measured towards similarly distant SDSS quasars, implying that results from optical- and NIR-selected quasars may be combined in studies of cosmological reionization. Also presented is a new NIR-spectrum of the previously discovered UKIDSS quasar ULAS J020332.38+001229.2, which reveals the object to be a broad absorption line quasar. The new spectrum shows that the emission line initially identified as Ly α is actually N v, leading to a revised redshift of Z=5.72, rather than z= 5.86 as previously estimated.

Original languageEnglish
Pages (from-to)97-104
Number of pages8
JournalAstronomy and Astrophysics
Issue number1
Publication statusPublished - 1 Oct 2009
Externally publishedYes


  • Cosmology: observations
  • Galaxies: quasars: individual: ULAS J020332.38+001229.2, ULAS J131911.29+095051.4-infrared: general


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