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

摘要

Optical and near-infrared (NIR) spectra are presented for ULASJ131911.29+095051.4 (hereafter ULASJ1319+0950), a new redshift quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared Deep Sky Survey (UKIDSS). The source has ,corresponding to ,which is comparable to the absolute magnitudes of the quasars discovered in the Sloan Digital Sky Survey (SDSS). ULASJ1319+0950 was, in fact, registered by SDSS as a faint source with ,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/NV emission line, which has a rest-frame equivalent width of 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 Lyoptical depth to ULASJ1319+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 ULASJ020332.38+001229.2, which reveals the object to be a broad absorption line quasar. The new spectrum shows that the emission line initially identified as Lyis actually NV, leading to a revised redshift of z=5.72, rather than z=5.86 as previously estimated.Key words: galaxies: quasars: individual: ULASJ020332.38+001229.2, ULASJ131911.29+095051.4 - infrared: general - cosmology: observations