title: The Discovery of a High-Redshift Quasar without Emission Lines from Sloan Digital Sky Survey Commissioning Data.
abstract: We report observations of a luminous unresolved object at redshift z=4.62, with a featureless optical spectrum redward of the Lyalpha forest region, discovered from Sloan Digital Sky Survey commissioning data. The redshift is determined by the onset of the Lyalpha forest at lambda approximately 6800 Å and a Lyman limit system at lambda=5120 Å. A strong Lyalpha absorption system with weak metal absorption lines at z=4.58 is also identified in the spectrum. The object has a continuum absolute magnitude of -26.6 at 1450 Å in the rest frame (h0=0.5, q0=0.5) and therefore cannot be an ordinary galaxy. It shows no radio emission (the 3 sigma upper limit of its flux at 6 cm is 60 µJy), indicating a radio-to-optical flux ratio at least as small as that of the radio-weakest BL Lacertae objects known. It is also not linearly polarized to a 3 sigma upper limit of 4% in the observed I band. Therefore, it is either the most distant BL Lac object known to date, with very weak radio emission, or a new type of unbeamed quasar, whose broad emission line region is very weak or absent.
authors.initials: X
authors.lastname: Fan
authors.initials: MA
authors.lastname: Strauss
authors.initials: JE
authors.lastname: Gunn
authors.initials: RH
authors.lastname: Lupton
authors.initials: CL
authors.lastname: Carilli
authors.initials: MP
authors.lastname: Rupen
authors.initials: GD
authors.lastname: Schmidt
authors.initials: LA
authors.lastname: Moustakas
authors.initials: M
authors.lastname: Davis
authors.initials: J
authors.lastname: Annis
authors.initials: NA
authors.lastname: Bahcall
authors.initials: J
authors.lastname: Brinkmann
authors.initials: RJ
authors.lastname: Brunner
authors.initials: I
authors.lastname: Csabai
authors.initials: M
authors.lastname: Doi
authors.initials: M
authors.lastname: Fukugita
authors.initials: TM
authors.lastname: Heckman
authors.initials: GS
authors.lastname: Hennessy
authors.initials: RB
authors.lastname: Hindsley
authors.initials: Z
authors.lastname: Ivezic
authors.initials: GR
authors.lastname: Knapp
authors.initials: DQ
authors.lastname: Lamb
authors.initials: JA
authors.lastname: Munn
authors.initials: AG
authors.lastname: Pauls
authors.initials: JR
authors.lastname: Pier
authors.initials: CM
authors.lastname: Rockosi
authors.initials: DP
authors.lastname: Schneider
authors.initials: AS
authors.lastname: Szalay
authors.initials: DL
authors.lastname: Tucker
authors.initials: DG
authors.lastname: York