The discovery of a high-redshift quasar without emission lines from Sloan Digital Sky Survey commissioning data
Fan, X H; Strauss, M A; Gunn, J E; Lupton, R H; Carilli, C L; Rupen, M P; Schmidt, G D; Moustakas, L A; Davis, M; Annis, J
WoS ID: 000084116600001
Scopus ID: 0041192905
We report observations of a luminous unresolved object at redshift z = 4.62, with a featureless optical spectrum redward of the Ly alpha forest region, discovered from Sloan Digital Sky Survey commissioning data. The redshift is determined by the onset of the Ly alpha forest at lambda similar to 6800 Angstrom and a Lyman limit system at lambda = 5120 Angstrom. A strong Ly alpha 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 Angstrom in the rest frame (h(0) = 0.5, q(0) = 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 mu Jy), 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.