Detection of a Lyα Emission-Line Companion to the [ITAL]z[/ITAL] = 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 q 0 = 0.5, where h ≡ H 0 /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 .