2003ApJ...596L..39S

We report an infrared 1-1.8 µm (J+H-band), low-resolution (R=450) spectrogram of the highest redshift radio-loud quasar currently known, SDSS J083643.85+005453.3, obtained during the spectroscopic commissioning run of the FLAMINGOS multiobject, near-IR spectrograph at the 8 m Gemini-South Observatory. These data show broad emission from both C IV λ1549 and C III] λ1909, with strengths comparable to lower redshift quasar composite spectra. The implication is that there is substantial enrichment of the quasar environment, even at times less than a billion years after the big bang. The redshift derived from these features is z=5.774±0.003, more accurate and slightly lower than the z=5.82 reported in the discovery paper based on the partially absorbed Lyα emission line. The infrared continuum is significantly redder than lower redshift quasar composites. Fitting the spectrum from 1.0 to 1.7 µm with a power law f_ν∝ν^–α, the derived power-law index is α=1.55 compared to the average continuum spectral index <α≥0.44 derived from the first Sloan Digital Sky Survey composite quasar. Assuming an SMC-like extinction curve, we infer a color excess of E(B-V)=0.09±0.01. Only ~6% of quasars in the optically selected Sloan Digital Sky Survey show comparable levels of dust reddening.