Detection of a Lyα Emission-Line Companion to the z = 4.69 Quasar BR 1202–0725

We report the detection of a nearby emission-line companion to the z = 4.695 quasar BR 1202-0725. Deep narrowband exposures on this field from the University of Hawaii 2.2 m telescope show a Lyα flux of 1.5 × 10-16 ergs cm-2 s-1. High-resolution imaging in the F814W filter band with the Hubble Space Telescope Wide Field Planetary Camera (WFPC2) shows continuum structure near the emission position, at 2.″6 northwest of the quasar, corresponding to a projected separation of ~7.5 h-1 kpc for q0 = 0.5, where h ≡ H0/100 km s-1 Mpc-1. We discuss possible explanations for the combined line and color properties. The ionization is most likely produced by the quasar, but, if due to underlying star formation, would require a star formation rate of ~7 h-2 M☉ yr-1.